They've said she moved to London and moved in with them years ago.
I always only had the impression that Brian (& Arthur) absolutely adore all the women/sisters in their lives (and all their kids...and Donal & Sophie Skehans kids!).
I get why people could find Brian an absolute dose, but some of the cynicism people are viewing his relationship with Aoife with or his reasons for wanting kids when he so clearly dotes on the other kids in his life I don't get.
Listen to his interview with Amy Huberman if you haven't already is all ill say!