What's the best aide situation to care for two parents with Dementia in their home, without my wife and I having to move in?

Both of my parents are 90, and Dad has taken care of Mom at home for the last 13 years, with advanced Alzheimer's. Six weeks ago, on their 67th Anniversary, and two months after falling, breaking his spine, and making a remarkable recovery, Dad tumbled backwards down the stairs, landed on his head and incurred a major brain injury. He has been in hospitals and now rehabs ever since, and literally overnight he has become someone who himself will need 24/7 care and has the kind of dementia associated with brain trauma.

Our wish is to bring him home to Mom and provide for both of them what he provided for her for so long. How many aides, and in what configuration, do we need to do this? Live-in? Two 12-hour aides, 3 eight-hour? Different people on weekends? Mom can be left alone in a chair, because she can no longer get up by herself, and is often asleep. Dad can already get himself out of his wheelchair at the rehab, but doesn't understand that he can't walk on his own yet, so he will need to be watched constantly. If there was only one aide present and the aide had to change or clean Mom, Dad could be a danger to himself. Yet having two aides round the clock seems unnecessary. Has anyone figured out a good formula for this situation that won't require my wife and I to move in, but perhaps live nearby to keep an eye on the situation and manage things?