To what extent does your children come first?

It is not a sacrafice. You need to stop thinking of it that way. You put your children's best interest first always. No exceptions,ever, if you are a good parent. If you need or want something you can try to incorporate these things into your life with your children. As far as having family undermine you, sometimes children can be taught that there are different rules at different houses. I had to do this with my parents. But be firm, and let your family know what rules are critial to you. They can follow them or choose to be distanced from you and your children.