Not sure if you’ve looked into it, but as I understand it, this is what the Control Rig feature is for, so maybe you should have a look at that. It’s currently experimental but I believe it is entering Beta as of 4.26. I have no experience with it myself so I can’t tell you whether it will be exactly right or how hard it is, but I believe it is probably worthwhile checking out.
Alternatively in the past I have triggered animations from different skeletal meshes that are interacting by using animation notifies this gives you control over exactly when you want to trigger an animation based on another animation, it’s not full proof but does work.