theredhen "Why is it that step children never seem to have to be the ones to compromise, while it's OK for any other child in the family to do so?"
because the step children (at least in the case of my ds1) already have to compromise all the time... in that they don't get to live with both of their parents which many/most of them would really want. whereas, again in my own experience, ds1's half siblings (2 my dc and 2 his dad's dc) get by far the best deal because they don't have to wait 2 weeks to see their dads, they get tucked in every night by their dads, etc."
Yes, but step children often have 2 rooms, 2 lots of toys, 2 lots of pocket money, 2 lots of xmas and birthday presents, not to mention extra presents from step parents family too. Whilst they might not see both parents everyday, what they do tend to get is much greater amount of quality time because parents who don't have their children all the time tend to do the mundane chores when the children aren't around so they get more time to concentrate on fun things with the kids.
My DS has 1 bedroom, sees his father for a few hours once a fortnight, has the second smallest bedroom in the house, has to get dragged along to do boring and mundane stuff, has to share all his stuff with step kids, has to sleep on a sofa at his Dad's. He has 1 parent ferrying him to clubs, paying for him and generally taking responsibility.
His step siblings, I feel, fare much better than he does and people tend to "pity" them more even though DS is a step child too and is exactly the same, but he doesn't benefit from everyone pussy footing around for fear of upsetting him.
I realise everyone's situation is different, but there are lots of advantages to being a step child in a lot of cases and making some non resident children share a room or sleep on a temporary bed is not the end of the world. Surely teaching children that they ALWAYS come first and that they never have to compromise is not the correct way to bring up decent, caring, understanding young people.
I am NOT saying that the OP should not have the children at all, but I don't understand why a compromise cannot be made.