Assuming the list of communities in FC2 is always comma separated, give this a try. I have not tested this and I may have missed some crucial info in your discussion with Richard Fairhurst.
fc1 = r"C:\myDB\FC1"
fc2 = r"C:\myDB\FC2"
fc1_fields = ["community", "ref"]
fc1 = {community: ref for community, ref in searchCursor(fc1, fc1_fields)}
fc2_fields = ["communityGroup", "refGroup"]
with updateCursor(fc2, fc2_fields) as fc2_cursor:
for fc2_communityGroup, fc2_refGroup in fc2_cursor:
refGroup = []
for community in fc2_communityGroup[0].split(","):
refGroup.append(fc1[community])
fc2_row[1] = ",".join(refGroup)
fc2_cursor.updaterow(fc2_row)