I am so sorry for what has happened. i live in south louisiana and it sounds like what happened twice down here last year.
first, don't feel guilty. i'm sure it's hard to leave him during the day but he's with your parents so he is well taken care of and loved. also, like you said, it's for his health.
he is uncomfortable at your parents' house, even in his crib? if it's been a big ordeal (which i'm sure it has been), this could also be a reason for lo not being comfortable. i'm sure that he feels the stress going on plus he's in a new house. this may not be very helpful but i would try my best to not stress out right now. i would assume that since you've stayed home with him, he's very close to you and if you feel stressed out about the house plus the fact that you feel guilty about leaving him during the day, he's going to mirror your emotions.
i don't have any suggestions besides trying to control your own emotions as much as you can at such a hard time. you have a safe place to stay and grandparents who love him and can care for him while you get your house taken care of. you may need to go back to the sleep training techniques you used when he was younger to help settle him at naps and bed.
i'll be thinking about you guys.
melissa