How to cope when a sibling changes within a relationship and you have doubts about it's longevity?

She’s always been well suited to relationships - but ultimately fiercely independent, career driven, vocal against having children, feminist, doesn’t believe in gender roles etc. However, she’s currently in a relationship with someone who comes from a traditional family with pink & blue jobs and has a child. In plenty of ways it’s a great relationship, but as someone who's known her all her life it’s also tricky to wholly accept - she’s spending weekends surrounded by screaming children in soft play areas, she does the majority of the food shopping/cooking/cleaning, confidence builders like fixing the car or her bikes are now mostly delegated to him, he’s supportive of her career but it seems like he doesn't understand how high she can fly in the way he would with a fellow man. There‘s also been other major issues within the relationship (intimacy, domestics, life plans, politics), which makes me question her happiness long-term. Some of the rushed milestones have also felt like a case of the ‘taxi cab theory’.

I’m focusing on the negatives here because that’s what I’m struggling with, there are also plenty of positives. My issue is, marriage is 100% on the table - it’s a matter of when not if, and it'll be coming sooner rather than later. I’m trying to have faith in their relationship and her choices, but I’m really struggling with the idea that I‘m supposed to stand up and celebrate their marriage when I’m feeling *this* off about the way things are looking. She knows I'm not sold on this as a marriage just yet, unfortunately my feelings still haven't changed since we discussed it and I don't know what to do.