Although I don't have an alter, I will sometimes go back and forth between my younger/past self and my present self. Have you ever tried, like the other said, leaving messages or notes for the other? I sometimes take video of myself talking to my younger/past self mindset saying things like, "Hey I don't know what you're going to do but so and so is your friend. Be nice to them, at least for me. I won't appreciate it and I'll slap you if you do something." or, "By the way, this person is coming over. Their name is ---" "Please be nice to my body today I really don't want to have to clean up after you. We share the same body so whatever harm you may do to yourself, you'll have to deal with it too."
I also suggest speaking with your spouse about how your alter acts, have him take video footage(hiding it from alter) so you can get a sense of actions, behavior, and guess at thinking process the alter maybe have.
Again, I'm sorry if this does not help since I personally do not have the same struggles but I hope someone else may be able to offer some useful information!