2 and 4 yo room sharing?

We have multiple family members visiting in November where oldest will be almost 5 and middle will be 2.5. To make space for everyone, I'm considering putting the 4yo on an air mattress in the room with the 2.5yo in her crib. Bad idea? They definitely tend to rile each other up. Family is coming on a Tuesday for a week. Should I start them together on the weekend to get used to it? Older one is in preschool so I'm worried about her not getting enough sleep. Alternative is to put my mom on an air mattress in the living room which I don't want to do because the (then) 9mo will sleep in our (large) master bath so my husband (who works weekdays) will have to shower in the main bath and wake my mom up early. Thoughts? Ideas I haven't thought of?