Nells Bells, you are my doppelganger! BTDT, burned the t-shirt.
I handled X's poor communication skills by texting or emailing both
of them the same message. For example, I'd email, "Hi Ex and Ex's SO: Jr. will be with you mm/dd from time a.m. to time p.m. I will drop him off at your house, you will return him to my house." Then I'd follow up with a text to both
, "Leaving my house to drop Jr. off. There in xx minutes."
In other words, the "main" arrangement would be in writing to both via email and then a follow up, if necessary by text, but always to both of them. This had several advantages:
We all had the same information, in writing;
Neither Ex's SO nor I had to deal with Ex's poor communication skills;
I didn't have to talk to either of them in person, so they couldn't grate on my nerves; and,
I took the initiative so I out-control-freaked the control freak by making the first move.
Saved my sanity more than once, let me tell you.