Husband gives his biological daughter special treatment compared to two sons that are not biologically his

TL;DR husband treats his biological daughter better than our two sons. What should I do?My husband has a 13-year-old daughter that he has raised her whole life. The mother of his daughter (drug addict, still has no rights to her children) had another son 3 years later, and although he was not dating the mother nor is he the biological father of his son, he decided to sign the birth certificate. He raised the son with his daughter just like he was his own (apparently, I don't know because I wasn't there). Fast forward years later and I am married to this man and I have my own biological son from a previous relationship. I have noticed my husband gives his daughter obvious special treatment compared to the two boys. If the boys ask for something he typically says no, but if our daughter asks for something he usually says yes. He denies giving her special treatment and gets really defensive when I bring it up. Like he'll practically do her chores for her because "those are wayy too many dishes for her to do by herself" but then wont lift a finger to help the boys with their chores. Today for instance, our daughter asked to go to the movies with her friend we said yeah because we assumed she had her own money left over from allowance. Turns out she doesnt, so she asked for money for the movie. I said okay but we only have $5 (tickets are $6.50.) He runs to the atm and takes out a $20 and asks me if thats good. I said she doesnt need that much, just give her $10. He says how about $15 instead? Snacks are expensive. I said i don't care if snacks are expensive she didn't ask us to borrow money until the very last second, $10 is more than enough. Plus her friend is the one who invited her so they should be buying the snacks. This is just one example of many. How do I navigate this? I'm so tired of fighting over the same ridiculous thing.Edit: I am absolutely aware how amazing of a person he is for signing the birth certificate for a child that is biologically not his. I admire that whole heartedly. However, these circumstances are not our children's fault. None of our children asked to be born and we should treat them all equally as gifts. Some of you have said well "as long as there's no abuse and they're being adequately taken care of..." absolutely not. Children deserve just as much love and nurturance as any other child, biological or not. Shame on some of you. via /r/Parenting https://ift.tt/2NJdS25