So Ruth is a Warren descendant... most likely, unless the person who called her out has a reason to lie. I think Rosemary potentially could be a descendant and is hiding it. This may be the reason she is the one always doing genealogy reports.
A lot of people have been saying that Ruth is Evan's grandmother, and I think this is likely as well. But one part of this theory doesn't really fit. Ruth is 92 in the present day of the show. Evan's mother Lauren was likely close in age to Tom, who is at oldest mid 50s. Ruth is far too old for her pregnancy to have been a scandalous teenage pregnancy, but it could have been an affair of some kind.
Alternatively perhaps we have a missing generation a