Catholic Encyopedia has:
On 12 June, 1595, Rahosa, the metropolitan, and the Bishops of Vladimir, Lutzk, and Pinsk met at Brest and drew up two petitions, one to Clement VIII and the other to Sigismund III. The former protested that they desired to renew the union concluded at the Council of Florence, saving always the Eastern customs and rites; in the latter the same desires were expressed, and it was added that the Ruthenian Church adopted the Gregorian Calendar.
… on 25 November, 1595, Pociej and Terlecki arrived at Rome with the decree of union of 2 December, 1594. The arrival of the Ruthenian bishops overwhelmed Clement VIII and the Roman Court with joy. The delegates were received with great honour; the pope and the cardinals discussed the conditions of reunion proposed by the Ruthenian episcopate, and ungrudgingly conceded that the integrity of the Ruthenian Rite should be maintained; it was also agreed that the “Filioque” should not be inserted in the Nicene Creed, although the Ruthenian clergy professed and taught the procession of the Holy Spirit from the Son. The bishops asked to be dispensed from the obligation of introducing the Gregorian Calendar, so as to avoid popular discontent and dissensions, and insisted that the king should grant them, as of right, the dignity of senators. To all these requests Clement VIII acceded. All obstacles having been removed, the union of the Rutheians with the Roman Church was solemnly and publicly proclaimed in the Hall of Constantine in the Vatican. Canon Wollowicz, of Vilna, read in Ruthenian and Latin the letter of the Ruthenian episcopate to the pope, dated 12 June, 1595.
newadvent.org/cathen/15130a.htm
Union of Brest, includes doctrines and avoiding confusion and discord:
- Since there is a quarrel between the Romans and Greeks about the procession of the Holy Spirit, which greatly impede unity really for no other reason than that we do not wish to understand one another - we ask that we should not be compelled to any other creed but that we should remain with that which was handed down to us in the Holy Scriptures, in the Gospel, and in the writings of the holy Greek Doctors, that is, that the Holy Spirit proceeds, not from two sources and not by a double procession, but from one origin, from the Father through the Son.
“5. We shall not debate about purgatory, but we entrust ourselves to the teaching of the Holy Church.”
- And if in time the Lord shall grant that the rest of the brethren of our people and of the Greek Religion shall come to this same holy unity, it shall not be held against us or begrudged to us that we have preceded them in this unity, for we have to do this for definite, serious reasons for harmony in the Christian republic [Poland] to avoid further confusion and discord.
fordham.edu/halsall/mod/1595brest.asp