This happened last year. I'll try to keep it succinct.
BIL and DH agree to go halves on their fathers milestone birthday. Weekend in sat big motor racing event. DH pays for tickets, BIL accommodation-a motor home. Around a grand each. All fine.
Few weeks before event, we find out BIL bought a £700 tent instead of booking a motor home as agreed. This saves him a few hundred and he gets to keep it but never oks it with DH. We think this is not on.
Closer to the event, SIL who is 6 months pregnant, decides she doesn't want BIL to go to the event due to risk of covid in her pregnancy. I'm not against this per se. But she wants whole thing rearranged til next year. DH and FIL however still want to go. They don't want the tent they never agreed to so want to hire a motor home as originally planned. To cut a long story short, BIL was never going to contribute to this or anything now he's not going and he bought himself a tent! In the end he doesn't contribute to his dads birthday event, expecting his dad and my DH to pay which they did. A smaller contribution would have sufficed.
This caused a big argument last year. I think they're incredibly selfish. Was IBU?