Seeker, I too think you are being very unrealistic here. I don't think you are a stepmother. I have 2 DSSs, and would feel very uncomfortable with them getting into bed with me and DP. I also have 2 DSs, and I know DP feels uncomfortable if they try to get into bed with us. We have all 4 children 50% of the time. Do you really expect that DP and I should never have sex in our own bedroom when the children are here, just in case one of them should wake up? Do you expect us to wait until all the children are at their other parent's house before we share any intimacy? Is it wrong to sleep naked in my own bed, just in case someone has a nightmare?
Unlike my own children, I also don't undress, dress, go to the toilet or share a bath with my DSSs, although I do all of those things sometimes with my own DSs. Is that also unfair?
I think there is a huge difference between having someone else's child over for a sleepover, and having step children who regularly/permanently sleep in your house. If I had a child over for a sleep over, I would expect that they might have a disturbed night's sleep/wake up very early/mess about - in which case, I'd have my pjs on, and DP and I would probably take the night off (!!). However, our house is our childrens' (all 4 of them) HOME, it is not somewhere they feel nervous or unwelcome. Remember it is also my home, and DP's home.
However, there are boundaries, and sometimes those boundaries are different when you have children and step children in the mix. The children's rights are not paramount - we are constantly juggling to try and make sure that EVERYONE's needs are met - those of the adults concerned, and those of the children. If DP and I always put the children first, in every decision we made, and so did their mum, and my exH, as you seem to want to suggest, then we'd be bringing up 4 very selfish children, who always expected their wishes and desires to take precedence over everyone else's. In a nuclear family (for want of a better expression), the children's needs are not always put above those of the adults concerned. In a step family there is an extra layer of complexity to that, and that's what I think you haven't understood.