Are you kidding me? I really hope this is just a fake post because if its not, you need to have your head examined. You would really send your vulnerable, defenseless 5 year old to stay in a house with a drug addict whose only been sober for 3 months? And for a whole week at that???
Assuming he has been clean for 3 months (and that's a big assumption), thats really not that long and relapses are quite common with addition. If he's still using then there is no telling what your child may be exposed to during that week...and if you think that grandma will step in to protect your child from whatever toxic behavior he may be exposed to then you're delusional. She may love her grandson, but she loves her son too. She's known him a lot longer, is prob desensitized by his habits and she's used to enabling/protecting him...after all, she's letting him live in her house, with no job and he's 35 years old...that says a lot.
And as for that husband...I would tell him to kiss my grits. He can stay mad for as long as he wants, but no threat of anger or hostility would scare me into putting my child at risk. I would find a drop in daycare center, spring break camp or another parent to help out for 2-3 days and maybe try to take 1-2 sick days to cover the full week.
Good luck
