Step parents and custody rights
I am soon to be married and my fiancee has two children from a previous relationship (he and the mother were never married). He has full custody of the children and the mom only has visitation and is ordered to pay child support (she voluntarily gave up custody last year). The children live with us and visit the mother only on weekends. After we marry, is it possible for me to get legal rights to the children? My fiancee is actually trying to get her visitation taken away completely, or at least reduced because she is unstable and he suspects that she is using drugs...she doesn't have a job or a car, and now she doesn't even have a place to live. The last time the children went for visitation my fiancee called to check on them and there were sleeping on a couch at her friends house. Under what circumstances are step parents granted custodial rights? Is it possible for me to just flat out adopt the kids when their biological mom is still in the picture? I know we should talk to a lawyer about this, but right now money is really tight and we just can't afford it. We're trying to navigate the system by ourselves, and so far my fiancee has done pretty well. 
Any advice would be greatly appreciated.
She would have to sign over
She would have to sign over her parental rights for you to be able to adopt.
Best thing we could come up
Best thing we could come up with was Power of Attorney. Basically, I have the right to stand in DH's place, and he has the right to stand in mine, in regards to our children. We have custody of all. My exH is not in my kids lives, aside from an occasional phone call to upset them, and BM sees her kids every other weekend. Therefore, I'm mom and he's dad, as far as our household is concerned.
As far as I know in my state,
As far as I know in my state, the biological parent has to be stripped of their parental rights before any other adult can be given parental rights to the children (You would be adopting them). In order for this to happen, the bio parent must have zero contact with the children for a year, pay no support towards the children for a year, or you must prove that the bioparent is abusing (emotionally, physically, or sexually) or is neglecting the children. You could become the children's legal guardian without having any impact on the biological parents rights. This can be contested, in which case you have to prove why it is in the childrens best interest for you to become their legal guardian, or uncontested, in which case the judge would simply grant you guardianship.