Blended families..

I struggle a lot with my bonus son. He is a super shy kid who never really got comfortable around my kids& i until recently after living together for a good while. Now he’s mouthy as ever. He doesn’t want to listen to anything i say & basically tells me I’m not the boss even if I’m talking to my own kids. His father & i struggle with parenting differences so i also can’t really parent him either. I know that may be another reason. I know this is normal for the situation. But what can i do? I want to be close to him & i want our relationship to be good. I’m just afraid this will last forever.