Unless you have a stepson and a bio son the exact same age, it is hard as a stepparent to know if you are treating them differently. Sometimes I feel like I am asking too much of my stepson, or giving him a hard time about something, but since my stepson is 10 and my bioson is 2, obviously there are very different expectations. You know what I mean? I can't saw "all the kids will clean their rooms, or wash dishes," of course, only dss does that. What I do, and maybe you could ask your dh to do, is I try to imagine how I would feel about it if it were my bio son. For example, my stepson likes to crawl under my bed and hide. For some reason, this bothered me. I felt like it was an invasion of my privacy, like I might have dirty clothes or something underthere. I tried to imagine in the future if my bioson was 10 and crawling under my bed, would it bother me? I was surprised to relize that no, it probably wouldn't bother me. So I made myself shut up and let dss crawl under my bed.
When you are faced with a certian situation, maybe you could ask your dh if they way he is treating his stepson is the way he is planning to treat his biokids when they get to be that age. Maybe it has to do with age with your dh (doesnt think any child of that age should be babied) or maybe he is being harder on your first child. If he can be honest, maybe that would help.