Hello! Please remember that my responses are informational only, we are not establishing a therapeutic relationship.
It sounds like you are dealing with multiple issues and losses:
1. Your struggle with infertility (which is very painful)
2. Your current health issues
3. The difficulty of being a step-parent (even in the best situations, issue arise from this).
What do you mean that your husband can be a "wimp" with them?
It sounds like a situation where your issues are colliding with their issues. They have to deal with the fact that they have a drug-addicted mother, you have to deal with the issues named above. On your side, you have resentment toward the girls, on their side they respond by being "lazy," perhaps attention seeking from Dad, and giving you grief over household issues. Even the acting like their mother might be a way of trying to have some kind of connection with the mother who gives them virtually nothing.
On top of those issues, you have the normal issues of late adolescence, where young people are trying to individuate from their parents anyway and become more independent. Trouble is, they still need their parents in ways that they won't in just a few short years.
I am not excusing any of their bad behavior, but I imagine that they have a lot of unresolved issues toward their mother. Therefore, whether they acknowledge it or not, there's a lot of pain there.
And, it sounds like you have some pain too. So my question back to you is --how can you be caring to them AND have your own needs met as well ?
--Do you need more from your husband (or is there something in your relationship that needs attention) ?
--What do you need to effectively address your health issues? (Rest, support from husband, more effective medical care)
--Do you need to grieve the fact that you never had your own children?
These are just some ideas. Both you and the girls need compassion and care.