Coming home for visits: Good idea or bad idea?

My 76 year old father was diagnosed with vascular dementia and moderate Alzheimer’s earlier this year. He also started having small strokes. This diagnosis came after several episodes that eventually lead to him asking us to take him to the hospital in the middle of the night. The most dramatic episodes seemed to stem from when my mother got sick last winter. She had some fairly significant medical issues that forced her to spend a month in hospital. When she was in hospital the rate of decayed in my fathers conative functioning was very visible. It seemed that he had no idea where or how to start taking care of himself i.e. what to do with mail (bills), how to feed himself etc. He was always very capable around the house over the past couple of years had becoming increasing confused over simple things. He eventually starting leaving burners running on the stove, starting electrical/wiring projects and not knowing how to finish them (getting electrocuted), falling and hitting his head while walking the dog. Doing plumbing jobs and causing the house to flood etc. The medical issues with my mother seemed to push him right over the edge. He eventually hit someone with his car and lost his driver license. The person was ok (thank god) but immediately following that event my father sank rapidly.
After a month in the hospital and family meetings we determined that my father needed to go into a care facility because my mother, although back home and partially recovered, does not have the ability to take care of him and her own issues as the same time.
Now my father is in a care home and trying to adjust. It is only a couple of miles from home so it is easy for my two brothers, my mother and myself to visit. My sister lives about 30 miles always so it is a bit more difficult for her to visit. This brings me to the point of the story. Although we have all been dealing with this in our own way we are all, with the exception of my sister, in agreement that my father cannot come home. He is very likely to burn the house down or work with power tools and injury himself, fall down stairs etc. My sister has been taking it upon herself to visit the care home and take my father out which we do no have exception with. She has, however, been brining driving him by his house which has been causing us all a great deal of concern. He seems to now feel he is working towards coming home and it is causing him great distress in the home after one of these events. The next day there are several phone calls to my mother from him asking/pleading for her to come pick him up. He is packing all of his belongings and putting them by the door. To make matters worse my sister actually brought him home while my mother was out (without her blessing) and sat around the table for a chit chat. She feels he is entitled because it is his home. We have asked to stop making these decisions on her own (unilaterally) but she will not. She feels she somehow knows better and that is it good for him. In the interim my mother is working at getting the home ready for sale so she can move to some type of supportive living facility.
Has anyone ever dealt with something like this? When, if ever, is it good to brining an Alzheimer’s patient to their old home for a visit that he can never really return to? How do we deal with our sister on this issue?
Any help or advice would be greatly appreciated.