Should I say something?

To preface my dad is an alcoholic. He has been my whole life. Due to his drinking I keep my distance but I have two kids and I want them to have a relationship with my dad but every time I have given him a chance to see the kids he’s drunk.

Thursday night was no different. I stopped over with my kids for only half an hour before I packed up and left because my dad was trying to pick a fight with my fiancé, my dad was cursing and saying the n word in front of my kids, and saying vulgar things in front of them to my fiancé.

I want to give him the benefit of the doubt and express to him how I’m feeling and tell him that if he can’t be sober around them, then I’m not bringing them around but my brother is telling me I’m being dramatic and it’s not that big of a deal. But it is, isn’t it? And I don’t want to just cut him out without at least giving him the opportunity to address this behavior. I just don’t know how to go about it without offending him and it turning into an argument.