Step family drama

A bit of background, my partner & his kids are not close. The oldest (21) gets in touch when she wants something or to find out why he hasn’t been in touch with his other two children (18 & 11). The Mother is causing a lot of problems, slagging my partner off on Facebook & her mother joins in saying he doesn’t deserve to live (his kids can see these posts!), she’s stopped him seeing the youngest before because I blocked her & had to add her as a friend again so he could visit.

The eldest daughter had a baby two weeks ago. I know her mother, two siblings, grandmother & other grandparents have all been to visit. They’ve had the baby out for walks & they’ve been out to shops etc. They finally text my partner asking when he was going to visit (we had both been messaging every other day just seeing how they were & explained we weren’t wanting to bombard them with visits) but said can he come alone and not bring me because due to Covid they need to limit the baby’s exposure & reduce risk of infection.... I totally kicked of! Shouting at my partner, crying, stomping around the house. Once I calmed down I said sorry & explained how upset I was, but did I over react?? Am I wrong to feel hurt & angry & like I’ve been deliberately excluded from a family thing?? I’m marrying this man & we live together! I’m not just a girlfriend, I’m part of his life, I’m part of their lives now. I feel like she just didn’t want me to visit and was using Covid as an excuse because I’m the only close relative not invited to visit.

Where do we go from here?? How should I handle it & act?? My partner and I are fine, talked it all out & everything, but I really don’t want this to affect our relationship at all.