If you want to go, then go. She's trying to have power of you, she only succeeds if you choose to give her that power.
Perhaps take a supportive friend with you so you don't feel so exposed to her efforts to start a fight.
Ignore her while you are there. Not going gives her power, biting back to her trying to fight gives her power.

Sounds like you may be a little too invested though to be honest. Stop trying so hard to make her like you. What does it matter? You can forge your own relationship with stepkids . I personally wouldn't be more involved with the kids than their own father, your DH, but if that is what you want then so be it, we each have our own standards

Why try to be civil when her evil manipulative lack of character does not warrant or allow it?

Own her toxic ass and have fun doing it. }:)

Go to practice, look your best, engage with the other parents who are there watching their own kids. Shine, be radiant, if BM pulls her usual bullshit just say something snarkily supportive like "Tsk, tsk, tsk, has it been a while dear? Maybe you should consider getting some and fixing that attitude."

You have tried being nice. Now it is time to be confident, assertive, and ... most definately not nice.

You are not causing the drama, BM is. Her problem not yours. Manage the situation so that your Skid's have absolute clarity that it is their BM that is the problem. My SS has always known who his REAL dad and who his REAL family is. He also knows who his StepDad is and who his BioDad is. I am the one who has invested in participating in his life and being a calm, confident, reliable influence. I am both his step dad and his REAL dad. Kids are smart, if you do what you always have done, be supportive, and be there for them they will know that it is their BM that is toxic and not you.

My Skid has never had to worry about his parents and family being supportive and participating in his life. When he graduated from high school his mom and I were there, my parents were there, and my ILs were there. A year later when he graduated from USAF BMT his mom and I were there, my parents were there, my brother and his wife and kids were there, and my ILs were there. His mom and I and my parents were also there for his tech school graduation, and his mom and my parents have been at all of his promotion ceremonies (I missed one of those due to being on an international assignment). He has never received so much as a congratulatory phone call from anyone in the Sperm Clan much less a card or their participation. When they call him it is to try to beg and manipulate him for money to help pay to support his three younger also out of wedlock sperm idiot spawned half sibs by two other baby mamas. Their non existence in his life is their call, not ours.

He knows who his REAL family is and so will your Skids.

Keep doing what you are doing..... without the guilt.

I never really 'get' why parents attend practice. IDK. I suppose as your SSs are age 3 and 5 that it is perhaps mandatory part of the very young kids and being able for them to participate. I'm going to assume a parent or another adult is suppose to be there when the kid is five (the kid is more like 9 or 13, totally unnecessary, games are one thing, practice quite another).

As you have the children 1/2 time (3-4dys on/off I believe you posted before) it's reasonable to think you'd be the one taking the kids to practice on Dad's time if Dad is still working or whatever. That to me isn't crossing boundaries or taking away from BM. All you're doing is seeing to it that the kids get to what the parents enrolled the kids in during Dad's parenting time. Nothing wrong in that. If BM wants to attend practice on Dad's time, that's on her. What I would not do is attend practice on days that are BM's parenting time (unless you go along because DH is going). That's BM's time to be parent/responsible adult. You don't need to attend every practice there is just to show the kids you support them in the activity.

You also do not need to be interacting with BM what so ever when you do attend regardless of if it's Dad or BM's parenting time. Sit across the room. Quietly minding your own business and enjoying the activity. Cheer the kiddos on. If it's BM's time, stay away from the kids. It's her 'shift' to be mommy. It's her responsibility to get them there, tend to the 3yr old if it's only the 5yr old participating, and to get them home. The kids will see you, know you came and watched and you can tell them all about how good they did, how proud you are, whatever when the boys return to your home during Dad's parenting time.

She obviously feels threatened by you. Not long ago you posted how one of the boys called you 'Mom' in front of her and how she reprimanded them. For Pete's sake, do not go out of your way to toss logs on her already burning fire. If you think BM doesn't appreciate all that you do for her boys now and/or all of the 'support' you shower onto the kids, just wait until she really has had enough of you playing SMOTY and decides to come down on you like bad on ugly. She could PAS these kids and make your life miserable. Do not put these kids in the middle of two warring women. Even if that's not your intentions (you just want to show the kids you love and support them), if you start inserting yourself into BM's time and territory (being called 'Mom' by her 3 and 5yr olds) you are hurting what you are trying to accomplish.