I would keep it as simple as possible, example, dad will be picking you up at 10 a.m and you will be returning home at 6 p.m, .( If they do not ask any additional questions you done., nothing else needs to be said) If they ask why they are not spending the night at dad’s I would try , it been decided that it’s best for you to be home at this time. I would follow it up with what will be going on when they get home. We will do pizza and movies, or we have to run errands, or whatever is current in your day to day world.
Do they know what alcoholism is? Do they know dad has a disease? Do they know that dad needs help with his disease? I have no idea what you have shared so far. I do not think it’s ever too young of age to talk about the dangers of drinking and driving, and not riding in a car with an intoxicated person, same concept as seat belts safety first. Buckle up.