Step children, bio children and &inlaws

So my steps child was the first born 11, then my SIL child 4, then my husband and I had a child whose almost 4.

How did your inlaws treat their grandkids? Equal? Favourism to one? If so, can you give my some insight on what exactly you and your children go through or how it works.

My mil treats the grandchildren very different and it's clear they don't have much desire for my daughter and I just don't understand why! I try to think of all the reasons why it is the way it is and try to justify my inlaws but i cant, My stepsons parents split before he was a year, they're great co parents and other then the wonder on what if they were together he has a pretty good life. I can sympathize that it's not the outcome anyone wants when it comes to separation and children but I also don't think that they should be treated and loved more then the other siblings. I used to think maybe it was age (when a baby) and that they'd come around but that's not it. Maybe it's my daughter? But I can't see how, she's great! Maybe it's me? I've never done anything to them! My family welcomed my stepson with opens arms, he doesn't get treated less than just because I didn't birth him. He treats my family the same he would with his biological family. My family have been involved way before I had children of my own and my parents would take my stepson just himself as I'm the only child. They've built a strong relationship over the years. So I don't think it's because they try to compensate for what my family does and how much they're involved with my daughter because it's equal.

I'm at my witts end, I love my husband but this is just not what I want for my daughter and its had me thinking of divorce, it's to stressful and sad. He doesn't stand up for his daughter, he doesn't even acknowledge this happens and acts like I'm crazy but then I'd loose my stepson and I've built 7 years and watched him grow and I can't even picture my life without him.