Petal and notadisneymum always seem to have good strategies.
Fwiw I think you are now on the right track?
I have a grown up daughter and 3 stepchildren, they have been in my life 10 years, as a family we have blended and I love them, there have been more good times than bad but it has been tough going. The children's mother loves them but they experience a chaotic life with her - low level neglect, years of nits, late nights, very poor diets, unwashed bedding but lots of treats, holidays, trips to New York, meals out, takeaways and private school for the youngest. To add to the chaos she had another child 3 years years ago and is still a single parent. We have never tried to compete with the treats, we try to structure their weekend weekends with us in a loving home with two parents who live by example, good food, clean beds, lots of sleep and Lots of laughter. The children have at times commented on the different life styles in the two households, I know they find it difficult, but they seem to benefit from the boundaries we set and being loved and nurtured.
We make decisions together, we support each other, we sing from the same hymn sheet where discipline is concerned and the children can never work out which of us is the weaker one or who is in charge. The youngest once asked "so who is in charge then?"
My advice to you is stick to your guns, decide on the outcome you want and do what is necessary to achieve it.
My husband would describe it as playing the long game, he would say goodness will prevail, he means do the right thing and things will turn out ok in the end.
I have rambled but I am trying to say fight for what you all need, stay strong for both the children and stick to your guns, always try to do the right thing and remember what children need most is boundaries.
Xx