Op, I feel like shaking you!!
You're letting your 22 month old toddler go off into the care of a cocaine user like it's nothing! Of course you need to know if he's rehabilitated or not, he could be driving drugged up, associating with criminals, what if the toddler found some?!
Some of his other behaviour sounds like shit parenting but the drug use is just dangerous and minimising the impact here is madness.
Communication by written form. Start gathering evidence of his parenting. Tell him you need formalized care arrangements, where his drug use and toxic mother will be discussed by impartial court members.
I think you've been so long in a Jeremy Kyle style group of people you're not thinking properly here, you're inviting trouble if you start letting this piss poor druggie dad orhis mum use your home as the place for building bonds with the kids, it's messy, confusing etc to kids. It's not normal for a reason. You think you're being accomodating but why are you permitting healthy boundaries to be crossed ?!
Seriously, wake up - courts would be on your side, the idea of an exclusively breastfed baby from being separated from the mother for 12+hrs is laughable.
But what on earth are you going to say when a judge asks you why you let him go off with your eldest in his care if you don't even know if he's taking cocaine still?!