Just to echo what others have said really. Step back, for your own sake.
You are not a bad person. You are a lovely person who horrible things have happened to. I am so sorry.
Quite possibly your own boys don't want to get so involved as they see how much your dad has hurt you, now and over the years, and they love you best and want to try and defend you from it, in their own ways.
He is in your brother's house now, so let your brother be the one to manage this. He can arrange ongoing care and future needs from his house. If your father needs to go into residential care for his own wellbeing, so be it. You can contact Adult Social Care in your area and ask for a welfare referral, citing the many safeguarding concerns you mention in your post. You have no obligation to agree to anything. Believe me - it will break you if you try to do this alone and under the circumstances and experiences you have - if you were to take it all on it may even be that your father ends up outliving you - I can feel the despair in your post and it's heart-breaking. You do not have to carry this burden.
Your dad can choose to return to live in his own house, with crises after crises. That's his right. But he then also has to accept the consequences of his choices. You do not. If he chooses to do things his way, however unwise, you can choose not to engage or enable the folly. Or do it at arms length - there's a flood, you can ring the plumber, but you won't go round to spend another evening mopping on all fours. He refuses to eat or drink or complains if you're going to leave? "That's your choice dad. Night night."
You cannot set yourself on fire to keep another person warm - even when that person is loving, compliant and appreciative, which is sadly not the case here. Your father has reached a stage where what he needs now outweighs what he wants. What he needs is a team of trained, professional people who can care for him safely and properly round the clock, not one single lovely but woefully unappreciated lady who has suffered terrible grief and is being unravelled piece by piece with unrealistic demands, guilt and torment.
Your life matters too. You deserve a happy life.
Have a look at the Cockroach Cafe in the Elderly Parents section of MN - lots of good help and advice there. Also the Stately Homes threads for children of difficult parents. You might also like to visit Out of the FOG - Index for support on dealing with the fallout of bad parental behaviour. It haunts many of us.
I'm sorry about what happened to your mum. That's horrible. I wish you and your sons happier times ahead. 💐 x