I'm not an expert on the Jerusalem church -- but my limited understanding is that its followers did not worship Jsus, but merely taught his teachings (ala the schools of Shammai and the schools of Hillel).

If they were observant Jews who did not worship Jsus but saw him as a teacher no biggie. If they further saw that non-Jews could follow his teachings as long as they, too, didn't worship a man as a god - no biggie.

The only issue I was responding to here was rather James was Jsus' biological brother.
And everything that Sarah tells you, listen to her voice. Genesis, 21:12