Galatians 1:2

καὶ οἱ σὺν ἐμοὶ πάντες ἀδελφοί, ταῖς ἐκκλησίαις τῆς Γαλατίας·

Verse 2 is a continuation of Paul's introduction.

και - and. We can tell that the 'and' goes with 'Paul' and not with 'God' because the following noun structure is in the nominative case.
οἱ - the (plural nominative)
συν ἐμοι - together with me. we would expect a noun to follow the article, but rather we have the descriptive phrase.
παντες - all (plural nominative)
ἀδελφοι -brothers (plural nominative) here is the expected noun.
so far : and the ones together with me, all the brothers.

ταις ἐκκλησιαις - the churches in dative case indicating that it is an indirect object (ie to the churches)
της Γαλατιας - the Galatians in genitive case indicating 'of' so of the Galatians.

Thus:
and the ones together with me, all the brothers, to the churches of Galatia.

The thing that I notice is that the Greek structure highlights the unity of the band of apostles/ brothers sending the letter. In English I get the sense of the letter being from Paul and the others being something of an afterthought. The structure of the Greek tends to draw the others into the picture more securely. But this may just be the way the structures of the languages work and have no particular significance.