I've never given this much detail about my grandfather before and it's really hard to do it now, but the OP's situation resonates with me and I feel for her so much. My grandfather, in his 70s and early 80s, suffered from Frontal Lobe Dementia brought on by long-term, severe alcohol abuse. He abused alcohol because he suffered from schizophrenia (and before anyone jumps on me for using this term, that is what the medical term was back then, when he was diagnosed originally in the 1950s/60s).
He made all our lives hell. Christmasses were horrendous. I used to vomit with fear whenever he was due to visit. As a teenager, I was terrified of him. He used to suddenly and violently grab me and assault me (grab my breasts, for example). He was clever though, and only did it when nobody else was in the room. He would openly touch himself at family gatherings. He beat up my grandmother, hit my mum in the face, constantly threatened to punch my dad, smacked me A LOT when I was little....
This is a very small snapshot into what his behaviour was like but I can only bear to write a little of it down.
He would vomit if he didn't have alcohol (OP mentions that her father cannot simply be denied alcohol, as his alcoholism is too far advanced for sudden withdrawal). Alcoholics don't just take themselves off to the bathroom to vomit in private. They just start retching wherever they are. so, in their lap if they're in an armchair. Into their dinner if they are sitting at the table. He was totally self-centered - all his needs had to be met and bugger everybody else. He would swear, call my grandmother the filthiest of names, scream, lash out .... it was just horrible and terrifying for everyone. This went on for years. I was constantly told by my mum to have compassion for him, and that it wasn't his fault ... but actually, everyone else in the family suffered horribly while his suffering wasn't ameliorated at all, so really there was no point to us seeing him or trying to help him. He'd have been suffering anyway no matter what we did - all he wanted was to sit in his armchair ranting, dribbling, spitting into his disgusting spittoon, pissing on the carpet and drinking a bottle of whisky (bloody Bells) a day while screaming and yelling a load of abuse at whoever dared come near him.
God, I'm shaking now. I still wake up on Christmas morning with that sense of dread in my stomach, just for a few seconds, before I remember that he has been dead for over 20 years.
@Tactful10 I completely understand why you and your family cannot deal with this type of behaviour. I think you are dealing with an impossible situation. You have to put your children first. They should not be anywhere near your father if you think it's inappropriate. Anyone who has the sheer bloody nerve to say that you need to learn some compassion, or who dares to judge you, is an arsehole needs to learn some bloody compassion of their own, frankly.
Sending you all the good wishes in the world, I am so so sorry you're having to deal with this.