Welcome here and to being a stepparent!

I think the role a stepmom plays in her stepkids' lives varies from situation to situation. When I was growing up, I wasn't close to my stepmother so she didn't play as big of a role in my life as I do in my SD's (stepdaughters) lives. Don't get me wrong- I was and am always civil to my stepmother, but no more.

A lot of us (me included) have dealt with the nasty, vindictive ex-wife. They badmouth our husbands and us to their kids and are anything but cooperative when our husbands (DHs) try to work with them/ obtain info from the/communicate with them. As a result, many of our stepkids are rude to us and have a lot of anger and hate in them towards the situation, us and their dads. It would just be so much better for everyone involved (including the birth mothers (BMs)) if all the adults could just find a way to get along.

For a long time, we had every other weekend visitation (EOW) with my SDs. Their BM would spew hatred, vindictive, untrue things about us to them and it (along with my DH's lack of ability to stand up to BM and SDs and correct them for their behavior) caused them so much unnecessary hurt, anger, hatred, and confusion.

I think the thing to do is to talk to your DH about the role you'll play in the family. Throughout the discussion, though, make it clear that, however big or small of a role you decide to play, a) he needs to demand that your stepkids treat you with respect, b) you expect him to discipline his kids and to give you a say in the rules for the stepkids and consequences for breaking them, c) you must be consulted in all things (note: in your home, you and DH are the final decision-makers. When he needs to make a big decision about the stepkids, for example about their schooling, medicine, or extracirricular activities, he must still consult you first and then make his final decision, THEN talk to BM and work something out. He might choose to incorporate your feelings in his decision, he might not. But most importantly, he'll have consulted you first.) d) He needs to set communication boundaries with BM. Those are 1) the communication must be about the kids only (that's an ABSOLUTE MUST) 2) Maybe they could exchange an email once a week to keep each other up to date on the kids' schedules, how the kids' week went, if the kids got in trouble in school or elsewhere that week, and they can call each other in emergencies. You both should work together in making a list of stuff she can call you about and stuff she can email you about, and he should email it to her. That way, it's crystal clear what she can/can't call about and what she can/can't email about. When the stepkids are over, he needs to show ALL of you affection. That way they'll see that just because Dad loves lovely lady doesn't mean he doesn't love them anymore. He should also spend 1-on-1 time with each of them because a) it's good for them and their dad and b) if BM tries to tell them he's a bad dad who doesn't care about them, they'll know the opposite. Last, but not least, he needs to tell her to grow up and act like an adult and tell her how dare she put the kids in the middle and not to EVER speak like that about you EVER again. I also HIGHLY recommend that you DO NOT communicate directly with her or go on pickups or dropoffs for the stepkids. You'll be saving yourself A WORLD of trouble.

Sorry this is so long, but this is what I've learned in my years of being a stepmom and it has been a HUGE sanity-saver for me. It's nice to meet you!