Oh Frankie, you poor thing. Selfish fathers are everywhere, and they are good at recognising goodness in others and using it (I have one too). He had no right to 'bequeath' you his nasty second wife! I have promised my daughters that I will leave them very little to sort out when I go - have already downsized, written will and decided on simple woodland (which they know about). If we truly care for our children we should put things straight before we go and not leave them with emotional time bombs to put right.
Sounds like you have had a rough time with this man's thoughtless choices and you have every right to walk away from this situation. It also sounds like you could do with some support, I hope you can talk this through with someone soon. You should not feel guilty, try to draw a line and give yourself permission to look forward, to enjoy your childrens' futures and not be held back by the past.