People were clannish back then so tended to marry within their own religion. Scots would be Catholic, Presbyterian or Episcopalian. Anglican patriots became Episcopalians I believe after the revolution, but prior to that Episcopalians should point more to Scottish ancestry. So if you can find out what church these people belonged to, it would be a good indicator if they were Scots or Welsh. Another indicator is who they married. Scots would more likely marry other Scots and the same for Welsh. There may also be clues with names so check the origin of first names of your ancestors and their families to see if there are any telltale ethnic names.