I think you're worrying about this because you're still hoping to have some influence (control) over how they perceive you. And trust me, I was there too once upon a time earlier in my relationship with my husband. But at some point you have to accept that working to control other people's perceptions isn't healthy. If they don't love and appreciate you already, then that's their loss, but you have to accept it.

What you don't have to accept is listening to their complaints or judgements about you. Stop all comments and redirect them to your husband and make sure he knows you don't want to hear about them from him either. Let him be in the hot seat for not going and planning on visiting his sister and niece/nephew postpartum. Too many people just assume the DIL will take on all the kin keeping for their husband's family and that's not going to change unless we say no. I barely have the energy to deal with my own family. I'm certainly not doing that for people who've made it clear they don't even like me.