I agree about the real soberlink, but I suspect that he and the new girlfriend will quickly get back to full time drinking, and he will have less interest than ever in seeing the kids. If he demands it for some reason, it is always supervised by his parents, who may be able to ally with you in not exposing them to him drunk or drinking? Time, sadly, may solve this for you since he sounds like he is already sliding down the slope again.
Main point is by fighting now, will that make him angry enough to push back and start demanding kids when maybe waiting carefully a little longer he will get distracted and back into his drinking world?