Bernia, I took care of my dad and dealt with the IRS because of a claim for back taxes. You have no legal obligation for his taxes or medical bills. Your mother did because they were married, that is why they went after him thought her. It took me many years even after calling and send his death certificate, they'd call and send mail. Each time I told them he was still dead, and they asked for his address so I gave them the cemetery and plot number. One man was shocked and told me that "this is a graveyard" and I told them yep, now leave me alone.
I would want to know where my father was going to be placed, and I'd go over the woman's head. Maybe if you call your congressman he'd be able to help.
Washington state also has Ombudsmen and they may be the next step to help you get your dad some help.
www.dshs.wa.gov/dbhr/ombuds.shtml
And as for boytoy? he'll have his own hell to go through one day.