Yes, twins run in families but not in every branch or every cousin's branch.

I think the chances are far more likely that John Looney wasn't a twin because (1) he wasn't baptised with Daniel, (2) his age given at burial would have made him b.c.1747, and (3) nowhere (that I have seen) said he was a twin.

I think the chances of his being a twin are so remote because of not being baptised with his "twin" that this shouldn't be included in your tree even as a query, unless you get solid evidence otherwise.

Sue