The people in question are those who seemed to be leaders.
This would be Peter, James, and John, possibly also including a few others. There were thus talks between leaders of the churches in Judea and the acknowledged leaders of the Gentile churches.1 The reference to Gentiles also serves to echo the call that Paul received to proclaim the gospel to Gentiles (Galatians 1:16).2
2 I went up because of a revelation and set before them (though privately before those who seemed influential) the gospel that I proclaim among the Gentiles, in order to make sure I was not running or had not run in vain.