When to call quits

Advice needed I’ve been with my partner for almost 3 years. We have a son together and a child each from previous relationships. Everyone got on fine before our son arrived and everyone was treated well and equal. The past year only my partner’s child is acknowledged by my partner’s family but through his mother instead of my partner, his family don’t try to contact us to see the family they go to my partner’s ex and spend the time with him alone. We’ve tried reaching out numerous times but our son we share has very little contact with the family and my other child is ignored completely. We’ve tried cutting contact with them but with the favourite child still having contact through the mum we have to hear about what theyve done and how we weren’t involved again. I’ve considered ending my relationship as I feel like the problem and family is very important to me. We are very close to my family and I hope that the family the kids all share treat them the same. My partner’s child has changed behaviour also towards me he doesn’t really speak to me when staying in our home.
Cutting them out and ignoring them hasn’t worked nor talking to them to try and better the situation I feel my only move is to end the relationship with my partner