You re going to get varied responses on here - re they have their own room, no space, my DCS should not have to compromise etc etc.
When it is practical and even if that means sharing I think Laloup sums it up - it needs to feel like their home - not like their visiting which in my mind is the start of the issue - they are not really wanted in the NRP home and considered an inconvenience, when they are not treated fairly.
In my house : DSD18 -and 14 share, DSS shares with my eldest was sharing with my youngest but did not work, ( chronic illness for mine caused sleep problems). We actually have a spare small room and no one wants it!!
Contrast that to my 2DCs - currently with their DF, they share a room - excellent.
When he was with his now ex DP - they shared a single bed in the laundry room, with the washing machine and tumble drier and all the cleaning stuff, whilst resident DCS had their own room and a playroom and the room they had shared they were kicked out of into the laundry room when new sibling arrived!
I will leave you to work out what that did for their self esteem!
Be kind and be fair - in your household, it is irrelevant what goes on in their other home.