Rowan as Rollo--brilliant. Maybe that's where she got that terrible nickname Rowly--doesn't somebody call her that?
I think that all the brothers' names are quite old English ones, though maybe Norman or some such. Think Piers Ploughman. Giles I think is medieval too--though I'm less good on male names than female ones. Anyway, I don't think they connote a French connection, just a very old family. Only Terrance seems sort of modern to me.