I don't want my kids to spend anytime over my in-laws house...?

because they have my drug addicted brother in-law staying with them at this time. He will out of the blue up and leave and not return or be heard from for several years at a time. This time that he came back HIV positive and won't take his meds properly. My concern is that all these issues, mostly his coming and going, is too much for the kids to keep dealing with. The kids don't know about the drugs or HIV. They just get really upset when he leaves. At this point I don't want my kids over there. I don't even want them to know that he is back this time. I don't want to keep the kids from their grandparents at all. I just don't want them to keep going through the emotional ups and downs with their uncle. I am more than willing to allow the children to go on outings with their grandparentS. Any thoughts or input would be appreciated. Thank you.

Thank you guys so much for responding. All of your comments were dead on! It would be impossible to select the "best answer".

About all you can do is drop by and take the parent-in-laws out to dinner, and quietly discuss the matter with them.
Don't sound like you are blaming anyone... be careful about that. But try to use words that are neutrally couched. Explain that you love them and your kids love them, but their emotional behaviors and experience has shown you that it is not good for the kids to be around that house as long as the BIL is hanging out.
You are also reluctant to expose your kids to a guy that is not very good at picking up after himself or his hygiene... particularly now that he has HIV.
Tell them you understand that they want to help this prodigal son, and you honor them for that, but putting the BIL in with your kids is not a good idea.
Suggest that they might consider just dropping by and taking the kids out to the park or something like that, then dropping them back at your place before heading home.... it may actually work out a lot more peaceful for them.

I do not blame you!
You have every right, and you are responsible for their security. doing nothing is about as negligent as it can get. Kids have a real propensity to be careless about fluid exchange, following people around eating their food, drinking out of their containers kissing, deadly serious situation. There is nothing more embarrassing than a dead kid unless it's a dying kid that you allowed to happen.

you have a huge right! not taking his medication properly is dangerous to your children, imagine if he does something stupid and ends up giving your children HIV. Talk to your in-laws about this and explain your safety concerns. tell them it not agaisnt them just the brother in law.