How do I get legal guardianship of my step children?

I have 4 beautiful step children, I usually refer to them simply as my children but not to confuse anyone they aren't biologically mine.

I am married to their father and when I first met them my husband was a single father and they haven't seen their mother for about 2 years at that point. Then, about two years into my husband and I's relationship she decided she wanted to see them 50/50 because she got a boyfriend. Then her car broke down and she didn't see the kids for 2 months. Then her boyfriend left her and now she hasn't seen the kids again. She's very erratic and she randomly pops up in their lives here and there.

She's never taken them to a doctor or anything. The other day I had to rush my youngest step daughter to the hospital because she needed stitches and there was a huge ordeal because I wasn't her actual mother and not a legal guardian. Even though I had her health insurance, PCP, literally everything because I signed her up for insurance and everything, there was a huge problem.

when I sign up my children for school it is also a huge problem even though my husband works during registration hours and their mom isn't ever there! I need to have the rights to my children because they are truly my own, I do everything possible that a mother would for them and I'm always there. I think this would be the right step to take