My youngest brother (29) puts very little effort in with our family. He has quite a needy, overbearing girlfriend who often dictates his schedule, and they spend a lot of time with her very close family who live near them. I haven't seen him since a family funeral in 2020 and we haven't spoken for at least 18 months - he rarely replies to my messages and never reaches out to me, so I just stopped. It's a shame, but just accepted he's happy living his own life, he doesn't owe me contact. He sporadically messages our other brother and dad back about football stuff, and speaks to our mum from time to time.
He's getting married in March, I've just received an email invite and link to the wedding website which is asking for donations for their honeymoon. They want to go to Japan in April for the cherry blossoms. What's a reasonable amount to contribute? He's my brother, but we have basically no relationship so not sure what to do. Aibu to only contribute about £50?