My mrs and her middle aged to elderly South Welsh Valleys relatives can't speak Welsh apart from basics picked up over the years.
But her family are now a mix of South & North Welsh by marriages over the last 2 to 3 decades.
So all the newest generation in their teens and 20s are perfectly bilingual...

Although we live across the Bristol channel, our home is dominated by the wife's proud/belligerent Welsh identity...

I think her family are resigned to tolerating me to some extent,
but would prefer if she'd married a good chapel going Welshman with a good job and a nice car...