I personally am really big against doubling up cousin names like that...I have a few cousins who's names I love but would never ever use as a first name for sure...possibly middle names but I would have to consider it a long time..lol
Lydia is an ok name in my book..I really liked it for about a year but after that it really dropped right off my list of fave names.
Therese is ok but I think of a New Yorker when I hear it...so just for that (not being a New Yorker myself) I wouldn't use it.