I can relate. DH and I are onlies. My mother lives in assisted living (her choice in CA), my father lives in an apt with aides coming in (Illinois), and we moved my MIL in with us last Oct. We built an addition for her, so other than a complete kitchen, she has her own space. My DH had her sell her car, since she wasn't doing a lot of driving.
The only issue when we moved her here was that DH didn't go early enough to start packing her up, so when he went to help her finish packing ( and he is one of those that if he doesn't know what to do with it, it goes), he rushed her and she got upset. She lived in a 3 bedroom, 1600 sq ft manufactured home to a 688 sq ft studio addition.
However, we are all doing better now, but she is not a very social animal. Therefore, she stays in the house a lot.