Ripeberry - i just want to send you a big hug. My father died after two years of hell with dementia and i know exactly how you feel. I remember when it all fell apart and my mum just coudlnt cope anymore social services being pretty useless actually. The social worker came and said to me, can you have your father live with you. Well there was simply NO way, i could have coped with that. I had my Eldest DD living at home and another on the way and my poor old dad would get so frightened he would lash out. I stood firm and eventually they did find my dad a care home.
This is too much for your Dad, and its also not fair on your mum, she needs professional care. My advice would be to start looking now as there are some great care homes out there, but as i found to my horror, some really bloody awful ones. Does your mum have a CPN? She could possibly organise some respite and get the wheels rolling for a care home. My Dad used to go to a day centre as well, that was a god send. My parents had no money and luckily (as it turned out) lived in council housing so the cost was covered by social services.
Contact the Alzheimer's society as they can be a great resource.
I feel for you i really do, its shit. There is no way to pretty it up so i wont bother, but help IS out there, you just have to stamp your feet HARD.
Dont even feel guilty for a second for not having your mum with you, it will not be fair on your children and it will be bad for your marriage, and your mum (when her normal self) would hate that. Your Dad has done what sounds like a wonderful job up until now - but its time for him to let go, i know this is terribly hard for you all, but you need to be objective, your dad cannot cope alone and your mum is a danger to herself. I totally empathise with the wandering, that was the most difficult thing to cope with.