I hear you - sending big hugs, it can feel very frustrating. XAH went from being a primary caregiver where DS meant a world to him to seeing him once/twice a month
Your children are lucky to have you
In my case XAH is sober, but backed out from taking DS12 to the lake in lieu of "going to the meeting" two weeks ago. So I just stopped saying anything to DS - we have supervised visits at grandmas - so we go and XAH takes all tests.
So if he does show up and is sober - it can be "surprise" for the kids.
My concern would be him showing up sober, and then getting drunk while they are in his care.