I haven't read everything yet, but here's the way I see it...
I'm a stepdaughter, I've been a stepmother, I'm a bio-mom/exwife, my son has stepparents now. In the end, it is all about the kids, IMO. They didn't ask for this dysfunctional family dynamic (and you can say what you want, but the truth is, it's dysfunctional....). It is and always has been my opinion that it is up to the adults to make things as easy and normal for the kids as possible. My parents didn't do that, so it was my vow that I would do everything in my power to make it easier for my stepdaughters and my son.
I never resented my ex for being an involved father. In fact, I was more likely to say we needed to do more than he was. The girls live 2 1/2 hours away, so we didn't make it to soccer games and stuff, but we made sure we made it to ballet recitals, school programs, etc. Now that we are divorced, we make sure we all get to his games when we can. I haven't missed any, my ex has only missed a couple.
Nowadays, my son has the biggest cheering section at his baseball games. It's usually me, DBf, DS#2, my mom, my stepdad, my ex, his wife, her son, my former SD's, my mommom and her husband, and for some games my dad, stepmom, 2 sisters, my other grandparents, my brother and his wife, etc. My 2 yr old started going to games and practices when he was about 4 months old. If it was chilly, he was bundled up and in the stroller. A few times when it was windy, we even went in the dugout. Last year was a bit more challenging because he was mobile and sitting in the stroller was NOT an option most days. But we made it work. My DBf works 2nd shift so he's not there for night games and practices, but my ex was normally there and he would help, not to mention the rest of my family. This year I've already offered my sisters $5 a game to help me with DS...they are 11 and 10 and can't wait to make a little money for playing with their nephew!
My point is, the entire stepfamily dynamic makes it more challenging, but to me, it's even more important to be supportive and work together BECAUSE of that. Your SS will remember you being there, he will remember you making sacrifices and he will appreciate it. Not now, but when he's older.

Your DH needs to tell the ex to get over it and find a way to deal. Your daughter will be fine...take her to the games, practices etc. It's all part of being a family, step or otherwise. My DS sometimes slept through the games, sometimes he got to bed later than usual. It didn't kill any of us.
