What Suz said times 10.
With an added huge dollop of "This is your husband's job, not yours" plus "What does HE think here?"
These are his parents. If he wants to see them, please accommodate that. Of course you need to set boundaries as well. I strongly recommend putting them up in a nearby hotel and presenting it to them as a treat for them. Limit the length of the visit. Plan some specific outings, too, so that there is not much "sitting around the house" time and also so they can interact with your kids in some structured way; some older adults (alcoholic or not) aren't great at knowing how to play with or talk with younger kids, so taking everyone somewhere to do something together, even just a family movie, can ease that tension.
Never leave your kids with them -- of course you can't. Does your husband get that or does he expect that you and he go out when his parents are there? If he thinks having the parents there means they babysit he needs to know that you are not comfortable with leaving the kids with them.
Does your husband acknowledge that they are alcoholics?
Does he agree that his mother drinks throughout the day?
Does he want them to visit, and he doesn't get your objections? Or does he feel they invite themselves and he's torn about it?
In other words -- you and he need to have a very tough and detailed talk if you have not already. He, not you, has to come to terms with it if his parents are alcoholics. He may be aware of it entirely but still want to see them -- just because they are alcoholics does not mean he must cut himself off and just because they are alcoholics does not mean they are bad humans or were horrible parents to him. He may feel, more than you do, that they are not going to be around long and he's willing to put up with the stress because he will regret it if he just rejects them. You see people who are sneaking drinks and making messes in your house and not trying to be close to their grandkids, but he may see the parents who raised him and were good to him and were good folks once.
I would encourage him to go visit them on his own, wherever they live, which gives him much more time to focus just on them (no wife and kids to think about) and that might be a big help to them and a way for him to better assess how they really are doing in terms of health, weight and drinking habits. I do stress that I would encourage him - not tell him "You have to go to see them because I won't welcome them here ever again." That statement would make this about you. Make it about THEM and their needs as they get older and his having a chance to spend real, uninterrupted time with them (if he wants to do so).
As Suz notes, they are not going to be around forever. Maybe they won't ever have a terrific, close relationship with your kids, and that rankles with you. But this isn't about you or the kids as much as it is about him as a son. So what does he want and need here, and can you focus on that?