<human>: My brother [27M] has been in a relationship with his girlfriend [27F] for 4-5 years. He has been shopping for an engagement ring and my family and I [25F] are struggling if we should tell him that we think he's making a big mistake. We don't like her because:
1. She does not respect him, especially in front of us and it's awkward to watch your brother be belittled in front of the entire family
2. We believe he could find someone who complimented his personality and supported him (instead of nagging and criticizing, especially in front of other people)
3. He seems happier and more carefree when she isn't around, when it's just us.

My sister says we should speak our minds "while there's still time". But I feel pretty strongly that if my family told me they didn't like my partner, I'd tell them to fuck off and never speak to them again. Our issue is that it's not only his happiness and "eternity" but the rest of our lives that we have to deal with her too.

I love my brother deeply. I cannot change his girlfriend. Should I tell him how I/we feel or should I shut up? 

Do you have a sibling-in-law that you hate? How do you deal with it? Do you wish you'd said something sooner? How do you navigate birthdays and holidays?

Condense the text into a few key points
<bot>: My brother's soon-to-be-fiance sucks, would you risk saying something and ruining your relationship with him?