You are asking a good question. It sounds like you are really weighing the pros and cons of the move, and are keeping your sister and brother-in-law's relationship as the priority. I also understand the reluctance to move your brother-in-law due to what may happen. I think the family needs to carefully weigh the potential toll against all the good that would come out of the move (such as the visits you mentioned from family and friends, which would be beneficial to your brother-in-law).

In my mother's case, the nursing home moved her (as well as the other residents who had dementia) two times to different rooms in different wings during renovations to the facility. Mom and some other residents with dementia seemed to rebound, but had difficult transitions. Other residents with dementia who seemed to be at a similar level as Mom did not handle the move well and their condition deteriorated. At least two died within a month after the move.

Here are some shareposts that I wrote about the moves (as well as a potential move that Dad and I considered for Mom to an Alzheimer's-specific facility) that may be helpful:

Moving Day: Creating Smooth Transitions for Your Loved One

How to Make a Smooth Transition

Moving Part III: The Importance of Stability and Structure

Helping Mom Through the Last Move

Should We Move Mom to the Newer Alzheimer's and Dementia-Specific Facility?

Take care and let us know what your family decides.

Dorian