My guess would be that
Matylda was either born in Poland or when the parents still thought they'd eventually return.
Sophie sounds like they decided to stay in England.
I dislike both names. I've always disliked
Matylda, it's so heavy.
Sophie is ok but terribly bland and, in contrast to
Matylda, almost weightless.
https://www.behindthename.com/pnl/109883