You pretty much have proof that he’s using it recreationally. He offered it to your son-and I think that we can assume that he’s not a medical professional!
It sounds like he probably does have epilepsy, and if it’s helping that, I don’t think it should be denied to him. Many of us have had to make this decision-for our kids and ourselves. After he had that bad seizure, did he contact his physician? It may be the wrong medicine for him. Would he neglect his health, in order to get the weed? (yes, it’s legal pretty much everywhere now, but if his doctor stopped prescribing it, it could become quite expensive!),
You should speak to him, and your daughter, about the dangers of driving under its influence! His offering it to your younger kids is a bit problematic. You could try forbidding it, but, sooner or later, it’s an issue they’ll all face…and have to decide upon. Just be there for them to talk to, and try not to be too judgmental. Anything a friend is doing, and it gets the parents worked up…well, forbidden fruit always has an added allure!
Good to see you posting here again, hope things are OK, and hope things aren’t too hard, for you, or your kids.
Still pandemic time…I hope not much longer. God Bless!