One of my brothers calls his wife's parents Mum and Dad. We come from a close family and our parents are still together ..... I find this weird and disrespectful to our parents.
DB's wife calls our parents Joe and Freda.... I call my DH's parents Bob and Maggie (and he calls my DPs Joe and Freda) and our sister also uses given names rather than "Mum and Dad" for her in-laws.
AIBU ? I would hate for my kids to be calling another woman "Mum"!
(The idea for this question came from the thread about step parents being called Mum and Dad....)