I think this is different than the OPs and many others situations where we see our stepkids EOW at the very least. Certainly if the kids were only seeing their dad a few times a year, than I can see how it would be inappropriate and unfair to not rearrange your cleaning day to spend time with the kids. I'm sorry your children have to put up with that!
In that case, the kids are more of a visitor to their dad's house, and therefore should be treated more like visitor. In my case, dsd lives here too. It is her house, she has her own room, her own things, etc. She is here frequently and considers herself to have 2 houses. Therefore, I don't feel like she should be treated like a visitor to our home.
Even though DSD is only with us at min. 4 days a month... we say she has two homes. She has her own room here, her own clothes, her own toys. She even has her own pet here. She is a part of this family, not a visitor.