Sorry, but you should give evidence about Paul mentioning members explicitly by name, and in that case you have only 2/3 times in Galatians + 1 time in Corinthians. It's very little evidence.>> Paul mentioned the Church of Jerusalem and members several times (1 Cor 16:1,3; 2 Cor 8:4, 13-15; 9:1, 12-15; Ga l2:1-10; Ro 15:25-26, 31) and acknowledged them as "saints" (1 Cor 16:1; 2 Cor 8:4; 9:1, 12; Ro 15:25, 26, 31). But despite these many opportunities in his epistles, Paul never said those were "in the Lord", or "in Christ", or just "brothers". However he used often these expressions to qualify other(s) as "Christian(s)": 1 Th 2:14, 3:8, 4:16, 5:12; 1 Cor 3:1, 4:15, 17, 9:1-2, 15:18,58, 16:19, 24; 2 Cor 1:21, 2:14, 17, 12:2; Php 1:14, 3:1, 4:1-2, 4, 10, 21; Phm 1:6, 8, 16, 20, 23; Gal 1:22, 3:14, 26, 28; 5:10; Ro 8:1, 12:5, 16:3, 7-13, 22<<
It is also far too early to expect that ''brothers'' indicates only Gentile Christians while the ''holy'' only the original apostles in Jerusalem.