I don't have a relationship with my younger brother. We haven't spoken for 12+ years, apart from small talk at occasional family events eg. weddings, funerals, the odd Christmas at our parents'. I'm 35, he's 29. No arguments or anything, we just grew up in a stressful, dysfunctional home, we were never close, live 3 hours apart, and have pretty much nothing in common. I did try with him for a while, but he puts zero effort in so I just gave up. I have no other siblings.
He's getting married in May. I don't really know his partner. I'm dreading playing happy families at the wedding, I don't really want to go. My mum asked me what I'm getting them for a gift, and suggested a cash donation towards a honeymoon in Asia. I was only planning on getting them a token 'gift' maybe a houseplant (a string of hearts plant) or something. If I gift cash it's got to be a substantial amount or it will look weird. Aibu to just get them a houseplant?
Also to note I'm not married (not interested in marriage/weddings personally) but have a long-term partner of 5 years. (Just in case anyone inevitably asks what he got me for my wedding).