I have a terrific idea. If his dad thinks that having alcohol and marijuana around as a "security blanket" is an okay thing, and his dad is assuming that he's going to come live with you even though you haven't agreed to it,
I suggest that he go live with his dad when he gets out of rehab.
as, in his own words, he would not be able to maintain sobriety without being surrounded by me and the kids.
You asked for opinions, lucy, and so here's mine: If you dont' want to do this, if you're not 100% sure that it fits your plan for your own happiness and that of your kids, if you don't feel strong enough to deal with a load of stress and pressure TEN TIMES what you're suffering now, then contact him immediately and make it clear to him he HAS to make other plans, that it's not going to work for you and the kids. If his dad has designated himself as your go-between, then tell him that way, but make it clear.
That kind of candor might take all the strength you have, but if he's relying on you to help him stay sober, coming into your sactuary without your permission, once again assuming that this is all about him and that your needs & wishes don't matter, then you may be in for a world of pain by not putting your foot down now.
Ten days of inpatient rehab (no offense to those who've gone through it) doesn't mean anything in terms of whether you can count on him to stay sober once he's forced his way back into your life again. There are people here who have welcomed home their A after months and months, just to see them start drinking again almost immediately.
And as you know, YOU are our primary concern here on this particular board
Wishing him luck with his sobriety, but wishing YOU self protection in this situation.