The beginning can be a bump

Every woman who gets married to a man, who has been married before and or has children from another relationship will know and understand this.
The ex. The woman before you.
Now I have no issues with my own ex, or his ex. Honestly I feel everyone should get along. We all have children and now these children are brother and sister. Step siblings can grow to be closer than blood siblings. So for this I really hold no hatred towards them. Mine or his.
But when the ex is the one with the problem, how do you resolve the issue?
I take a big role in the house here, when 'S' can't make it to an event, I go in his place. When he can't attend a meeting or pick up the children, I do it in his place. I volunteer at the school and this will will take part in the pta.
I do this because I feel it is important for the children and their father to know I am and will always be there for help and support.
But recently, I feel as though it angers the ex, more so now that she found out about the marriage.
So how do you resolve this? I have thought about that a lot.
I have tried to invite her for coffee, to discuss the roles we both share. I know from experience that some things, a parent wishes to teach their children rather have someone else do it. Riding a bike, makeup, even the time of the month (for the young ladies) and my views is to always be honest, so of asked a question I will be honest.
This isn't wrong, but I don't want to step on toes.
She of course has not taken me up on the offer.
In at a lost, at this point, and I'm sure I will be for a while.
But I am also smart and know and realize what some women are capable of.
In many relationships the ex will find ways to cause 'drama'. This isn't because they want the now ex back, but from mere anger. Women do this a lot, to jeopardize the happiness if the other woman, because she herself is not happy.
If you experience this, as I do, best thing to do is just smile.
Do not let it get to you, and remember they are an ex for a reason