Very brief background: my brother got divorced when my neice was about 8 and has been a shit Dad ever since particularly since his girlfriend has been on the scene. DN is 17 now & knows full well her Dad has effectively choosen his girlfriend over her & how useless he is - they see each other every few months at best despite living a few miles apart & that's usually when we go to visit & arrange a family meal. DN has also distanced herself from our parents as they fail to see the problems & DN she got sick of hearing crap like 'what a great Dad you've got isn't it a shame you're mum took you away from him' 
So, we met up with my brother last week & found out he got engaged a few weeks back & is planning a big 'adults only' piss up wedding in Ibiza next year. I don't know whether I'm more shocked that he hasn't told his daughter he's engaged or that they would choose to get married & actively exclude their own children (she has 2 girls age 14 & 16). When I asked my bro when he planned on telling DN he got all shirty & told me to butt out as did our parents 'he'll do it in his own time' . A week later she still didn't know so last night I ran DN's mum to ask her opinion & we agreed she'd tell her. DN later texted "thx for telling me love u" so I'm happy I've done the right thing by her, but my parents & brother have hit the roof saying I had no right, it's none of my business etc 
So, AIBU in not waiting for my brother to telll his only child he's getting married?