Grandkids dad has become raging alcoholic

Hi I believe you are in the US from some of the words you use, so the laws and services will be different from those in the U.K. however I know that there will be a form of social services and I think you referred to it in your post as CPS? I think if you have real worries about the conditions and emotional/ physical safety of the children you really should contact them especially as it sounds as if your step daughter is unable/unwilling to leave him or report him herself? She is a victim of domestic abuse!
You cannot realistically continue the current arrangement and to be honest even with one of you there 24/7 you cannot watch over each of the children every minute of the day.
Research has shown that children exposed to domestic abuse are themselves traumatised and likely to suffer mental health problems. This situation will harm the kids if left unchecked.
Sorry to be the bearer of bad news!

Emotional abuse is as concerning as physical abuse and should be stopped as soon as possible. I worked as a Senior Nurse for Children Protection for many years so I know just how damaging it can be. Please refer your grandchildren to Social Care (previously known as Social Services) before there is more damage. You can do this via the NSPCC website anonymously or directly to SC, again anonymously if you wish. If the children need to be removed Social Workers will always look to place them with family first providing you haven’t known about the abuse for any length of time and ignored it by not reporting it. If it drags on you could be seen as colluding with them. You are dreading about dealing with the drinking.....just think how those poor innocent children feel. We all have a duty to protect children and it’s something we all must do.

I m guessing this is a US poster not that it makes any difference except the help that can be expected may be different
Would your step daughter not take the children and leave him either going to a refuge or to you 7 hours away as his actions are brutally abusive, even if he hasn’t used physical violence so far, although you don’t know that for sure, and emotional and threatening abuse is every bit as bad and she and the children will be badly affected if they don’t get away
How is your wife treated when she is there?
This can’t continue with a drunken bully for a father they have to get out with your help

Rocky55 what a bloody awful situation, if you did take on the children (assuming that you could, legally) I think that there would be allowances available to you to help wit the costs of their care.

Sorry not to be able to be more help, but sending every good wish to you all.