On the stepson thing, at the end of the day, you're going to have to discuss this with your good lady.
However, equally, don't assume he will always be this way. There will be other factors that will trigger his wanting to change too.
It sounds like you want him to change instantly. This is not going to happen. Have a think about what you want, and then plan how you will go about achieving that.
I have 3 stepkids (well, they're all adults and parents now). I got to know them as teenagers. One (youngest) took to me quite quickly. One (eldest) never took to me at all, however has mellowed the past 4-5 years. The middle one has always been ok with me, and we get on very well, but has been distant from both of us for a couple of years.
I've always accepted that I can't make any decisions, and can't contradict their mum. That would be lethal. And it has always been hard for their mum, as she is always in the middle. It can't be good for her to constantly have the 2 people she loves most in the world constantly moaning to her about each other.
I always accepted from the start that mrs jelly would have the final say on anything parenting wise. I've never contradicted her, although we can disagree, and she will hear my concerns. However, her decisions have always been final. You're likely to need to accept that, and you will need to make some significant compromises.
I have always tried to be a friend first to her kids. I have always been honest with them, including when there are things that concern me. Importantly, they have always known that I want the best for their mom. I think a lot of the acceptance from them has come from having their moms best interests at the key of as much as I can do.
There's no doubt it has been challenging, for all of us. Equally, it has been hugely positive for all of us too. It's a very gradual, and evolutionary thing. There is no magic switch. It's a daily effort, but one that is worthwhile.
In the almost 17(!) years we have been together, we've now got to a stage where the youngest prefers to think of me as her dad, and won't correct anyone who mistakes me for her real dad. I'm not supposed to know that she likes it when people do that.
All that said, their mum comes first, to all of them.