Śrīla Raghunātha dāsa Gosvāmī has described Sanātana Gosvāmī in his prayer Vilāpa-kusumāñjali, verse six, where he has expressed his obligation to Sanātana Gosvāmī in the following words:
vairāgya-yug-bhakti-rasaṁ prayatnair
apāyayan mām anabhīpsum andhamkṛp
āmbudhir yaḥ para-duḥkha-duḥkhī
sanātanas taṁ prabhum āśrayāmi
"I was unwilling to drink the nectar of devotional service possessed of renunciation, but Sanātana Gosvāmī, out of his causeless mercy, made me drink it, even though I was otherwise unable to do so. Therefore he is an ocean of mercy. He is very compassionate to fallen souls like me, and thus it is my duty to offer my respectful obeisances unto his lotus feet." Kṛṣṇadāsa Kavirāja Gosvāmī also, in the last section of the Caitanya-caritāmṛta, specifically mentions the names of Rūpa Gosvāmī, Sanātana Gosvāmī and Śrīla Jīva Gosvāmī and offers his respectful obeisances unto the lotus feet of these three spiritual masters, as well as Raghunātha dāsa. Śrīla Raghunātha dāsa Gosvāmī also accepted Sanātana Gosvāmī as the teacher of the science of devotional service.
(Sri Caitanya Caritamrta-----1:5:203-----purport).

The actual purpose of Lord Caitanya's stay at Vārāṇasī after coming back from Vṛndāvana was to meet Sanātana Gosvāmī and teach him. Sanātana Gosvāmī met Śrī Caitanya Mahāprabhu after the Lord's return to Vārāṇasī, where the Lord taught him for two months about the intricacies of Vaiṣṇava philosophy and Vaiṣṇava activities. After completely instructing him, He sent him to Vṛndāvana to execute His orders. When Sanātana Gosvāmī went to Vṛndāvana, there were no temples. The city was lying vacant like an open field. Sanātana Gosvāmī sat down on the bank of the Yamunā, and after some time he gradually constructed the first temple; then other temples were constructed, and now the city is full of temples, numbering about five thousand.
(Sri Caitanya Caritamrta-----1:7:160-----purport).

When Rūpa Gosvāmī and Sanātana Gosvāmī went to Vṛndāvana, there was not a single temple, but by their preaching they were gradually able to construct various temples. Sanātana Gosvāmī constructed the Madana-mohana temple, and Rūpa Gosvāmī constructed the Govindajī temple. Similarly, their nephew Jīva Gosvāmī constructed the Rādhā-Dāmodara temple, Śrī Gopāla Bhaṭṭa Gosvāmī constructed the Rādhā-ramaṇa temple, Śrī Lokanātha Gosvāmī constructed the Gokulānanda temple, and Śyāmānanda Gosvāmī constructed the Śyāmasundara temple. In this way, many temples were gradually constructed.
(Sri Caitanya Caritamrta-----1:7:164-----purport).

Similarly, Rūpa, Sanātana and Vallabha were also given the title Mullik. Mullik means "lord." Just as the English government gives rich and respectable persons the title "lord," so the Muslims give the title Mullik to rich, respectable families that have intimate connections with the government. Thus the title Mullik is found not only among the Muslims but also among the Hindu aristocracy. This title is not restricted to a particular family but is given to different families and castes. The qualifications for receiving it are wealth and respectability.
(Sri Caitanya Caritamrta-----1:10:84-----purport).

Sanātana Gosvāmī and Rūpa Gosvāmī belonged to the Bharadvāja-gotra, which indicates that they belonged either to the family or disciplic succession of Bharadvāja Muni. As members of the Kṛṣṇa consciousness movement we belong to the family, or disciplic succession, of Sarasvatī Gosvāmī, and thus we are known as Sārasvatas. Obeisances are therefore offered to the spiritual master as sārasvata-deva, or a member of the Sārasvata family (namas te sārasvate deve), whose mission is to broadcast the cult of Śrī Caitanya Mahāprabhu (gaura-vāṇī-pracāriṇe) and to fight with impersonalists and voidists (nirviśeṣa-śūnyavādi-pāścātya-deśa-tāriṇe). This was also the occupational duty of SanātanaGosvāmī, Rūpa Gosvāmī and Anupama Gosvāmī.
(Sri Caitanya Caritamrta-----1:10:84-----purport).

The genealogical table of Sanātana Gosvāmī, Rūpa Gosvāmī and Vallabha Gosvāmī can be traced back to the twelfth century Śakābda, when a gentleman of the name Sarvajña appeared in a very rich and opulent brāhmaṇa family in the province of Karṇāṭa. He had two sons, named Aniruddhera Rūpeśvara and Harihara, who were both bereft of their kingdoms and thus obliged to reside in the highlands. The son of Rūpeśvara, who was named Padmanābha, moved to a place in Bengal known as Naihāṭī, on the bank of the Ganges. There he had five sons, of whom the youngest, Mukunda, had a well-behaved son named Kumāradeva, who was the father of Rūpa, Sanātana and Vallabha. Kumāradeva lived in Phateyābād, an area bordering Bāklācandradvīpa in East Bengal (now Bangladesh). The present-day village of Prembagh, which lies near Ramshara in the Jessore district of Bangladesh, is said by many to be the site of Kumāradeva's house. Of his many sons, three took to the path of Vaiṣṇavism. Later, Śrī Vallabha and his elder brothers Śrī Rūpa and Sanātana came from Candradvīpa to the village in the Maldah district of Bengal known as Rāmakeli.
(Sri Caitanya Caritamrta-----1:10:84-----purport).

Actually, it is to be understood from the statement of Sanātana Gosvāmī that Śrī Rūpa Gosvāmī and Vallabha went to Vṛndāvana under the instructions of Śrī Caitanya Mahāprabhu. First they went to Mathurā, where they met a gentleman named Subuddhi Rāya, who maintained himself by selling dry fuel wood. He was very pleased to meet Śrī Rūpa Gosvāmī and Anupama, and he showed them the twelve forests of Vṛndāvana. Thus they lived in Vṛndāvana for one month and then again went to search for Sanātana Gosvāmī. Following the course of the Ganges, they reached Allahabad, or Prayāga-tīrtha, but because Sanātana Gosvāmī had come there by a different road, they did not meet him there, and whenSanātana Gosvāmī came to Mathurā he was informed of the visit of Rūpa Gosvāmī and Anupama by Subuddhi Rāya. When Rūpa Gosvāmī and Anupama met Caitanya Mahāprabhu at Benares, they heard about Sanātana Gosvāmī’s travels from Him, and thus they returned to Bengal, adjusted their affairs with the state and, on the order of Śrī Caitanya Mahāprabhu, went to see the Lord at Jagannātha Purī.
(Sri Caitanya Caritamrta-----1:10:84-----purport).

Śrī Sanātana Gosvāmī is described in the Gaura-gaṇoddeśa-dīpikā (181). He was formerly known as Rati-mañjarī or sometimes Lavaṅga-mañjarī. In the Bhakti-ratnākara it is stated that his spiritual master, Vidyā-vācaspati, sometimes stayed in the village of Rāmakeli, and Sanātana Gosvāmī studied all the Vedic literatures from him. He was so devoted to his spiritual master that this cannot be described. According to the Vedic system, if someone sees a Muslim he must perform rituals to atone for the meeting. Sanātana Gosvāmī always associated with Muslim kings. Not giving much attention to the Vedic injunctions, he used to visit the houses of Muslim kings, and thus he considered himself to have been converted into a Muslim. He was therefore always very humble and meek. When Sanātana Gosvāmī presented himself before Lord Caitanya Mahāprabhu, he said, "I am always in association with lower-class people, and my behavior is therefore very abominable." He actually belonged to a respectable brāhmaṇa family, but because he considered his behavior to be abominable, he did not try to place himself among the brāhmaṇas but always remained among people of the lower castes.
(Sri Caitanya Caritamrta-----1:10:84-----purport).

In the Madhya-līlā, Chapter Nineteen, the device adopted by Sanātana Gosvāmī to get free from government service is described. He served a notice of sickness to the Nawab, the Muslim governor, but actually he was studying Śrīmad-Bhāgavatam with brāhmaṇas at home. The Nawab received information of this through a royal physician, and he immediately went to see Sanātana Gosvāmī to discover his intentions. The Nawab requested Sanātana to accompany him on an expedition to Orissa, but when Sanātana Gosvāmī refused, the Nawab ordered that he be imprisoned.
(Sri Caitanya Caritamrta-----1:10:84-----purport).

When Rūpa Gosvāmī left home, he wrote a note for Sanātana Gosvāmī informing him of some money that he had entrusted to a local grocer. Sanātana Gosvāmī took advantage of this money to bribe the jail keeper and get free from detention. Then he left for Benares to meet Caitanya Mahāprabhu, bringing with him only one servant, whose name was Īśāna. On the way they stopped at a sarāi, or hotel, and when the hotel keeper found out that Īśāna had some gold coins with him, he planned to kill both Sanātana Gosvāmī and Īśāna to take away the coins. Later Sanātana Gosvāmī saw that although the hotel keeper did not know them, he was being especially attentive to their comfort. Therefore he concluded that Īśāna was secretly carrying some money and that the hotel keeper was aware of this and therefore planned to kill them for it. Upon being questioned by Sanātana Gosvāmī, Īśāna admitted that he indeed had money with him, and immediately Sanātana Gosvāmī took the money and gave it to the hotel keeper, requesting him to help them get through the jungle. Thus with the help of the hotel keeper, who was also the chief of the thieves of that territory, Sanātana Gosvāmī crossed over the Hazipur mountains, which are presently known as the Hazaribags. He then met his brother-in-law Śrīkānta, who requested that he stay with him. Sanātana Gosvāmī refused, but before they parted Śrīkānta gave him a valuable blanket.
(Sri Caitanya Caritamrta-----1:10:84-----purport).