How have you overcome resentment towards your situation (particularly where BK's are involved)?

I have two stepchildren who stay EOWE and one night during the week. They're a handful, but overall great kids and we get along really well. There's no conflict whatsoever with BM, aside from some frustration towards the way she parents. Nothing major, but my opinion is that her approach reinforces behaviours my partner and I are trying to help them overcome. However, I'm really struggling to adapt to the dynamic and at times, I can't help but feel resentful.

I wrote and deleted a paragraph explaining all the reasons I'm frustrated, because ultimately there's nothing that can be done about it. SO is a great parent, and we can't control what BM does during her time. A lot of it is just kids being kids. A large reason for my resentment though is feeling like my LO (6 months) takes a backseat when they're here because of the time/attention they both require. It's feeling like his whole routine has to go out of the window for the days we have them. It's not feeling like I can give him the life I want because of limitations on location, the financial support SO provides BM because she doesn't want to go 50/50 (despite us also having to fund a larger home so they have their own rooms here), not being able to take LO away on holiday/trips out because it's unfair to the SK's (my frustration here being that SK's get to go away just with their BM, why does my LO have to share absolutely everything he does with them?). There have been compromises (i.e. we can take LO away, but let's do something with the SK's too), but it just feels like everything has to be centred around them despite us leading a completely different life the majority of the time.

I know their time with their Dad is very limited, and I feel so conflicted because I want the very best for them. I want them to have a great childhood and to support my SO, but I have such... what can only be described as sometimes irrational 'Mum rage' towards the whole dynamic because I want to give my LO the world and I don't feel like this situation allows me to. I didn't feel this way before I had my son.

My partner is great, but one point of conflict is him not understanding the way I feel. We both have step Dad's who arguably do love us as their own, so he uses them as an example despite the situations being entirely different. He thinks everyone should (and believes the majority of people do) love their stepchildren as their own. I've categorically told him I can't see myself ever seeing them as my own, or loving them in the same way as my LO, but I will always care for them, treat them as equally as I can and be a positive role model in their lives, but sometimes I feel like I'm having to push down how I'm feeling.

Has anyone else found a way to overcome the resentment?