I'm sorry for your losses.
I don't think that you need to make a snap decision, regarding your mom's family.
Right now you are sad and hurting. Please don't distract your grief by focusing in on
what other family did, or did not do. That won't be helpful to you.
In time you may actually WANT to be part of your mom's families' lives. Remember,
they share so much of your mom's history. Consider what your mom would want you to do, too, that may be helpful. As you well know, family is important, and I think it's especially important for young children.
Again, my condolences. It's such a great loss and you are a young woman, I get that.
My heart goes out to you. Please, though...don't burn your bridges. Just get through each day the best you can and get support from whomever will give it to you. If you need to, attend a local grief group.
God bless you.