Hi, no experience of shared rooms in CH but a couple of negative questions..... bearing in mind that Dementia is a potentially degregading illness, would you want your parent to been seen by a "sharee" or their visitors in a state of undress/unclean/ distress or to witness their roomie is a similar state?
And...even if they get on initally, what if they fall out, fall out with visitors, squabble over possessions or what if the roomie died, would your relative want someone else in the room?
As a very temporary measure, if it is the ONLY suitable home, and if it is written in the care plan that a single room must be offered asap, then I might be prepared to accept....but it is a big IF.