should I leave it alone?

So my MIL lives 2 hours away from us and I've made sure for the year that we lived this far apart that we're down there at least every other holiday. Just to be fair. So I asked my dh if we were going down tomorrow for the 4th. He says no. Turns out his feelings are still hurt because his mom didn't come to the baby shower for ds. Which we made sure was planned early to give her enough time to come. On top of that she didn't come when I went into labor. And he really wanted her there. She did come up right before they discharged Me 2 Days Later and took our daughter back home with her because I ended up having complications. She saw the baby again when we picked up sister. Then about a month after ds was born dh find out his mom and aunts were in the city we are in. And they didn't tell him. His feelings are hurt because he knows for a fact his mom never missed anything when it comes to his brothers kids. Which I know is true because she's all the time posting stuff about what she got his kids. And it's really getting to DH because she hasn't gotten anything for baby. Which to me it's not a big deal because whatever my baby needs or wants I got it. But it bugs my dh bc he sees the favoritism happening again. I just don't know if I should push my husband to go see them or just let him go when his ready. I'm just scared that his family is going to think it's my fault we're not going down there. But I don't feel like it's my place to tell them why he's upset. His brother was always the favorite. But he didn't think it would carry on to the grandkids. But now that he feels like it has he just doesn't want to be around them.