Unless he’s paid for it, it’s got f*ck all to do with your sisters husband
My mother used to tell me I ‘treat myself very well’ because I would bring my then teenager for a bite to eat after their therapy session to give them a non pressured environment to offload anything that came up in therapy if they wanted to….. coincidentally that’s around the time I started telling people that unless they were bankrolling my life, it was nothing to do with them how I spent the money I earned