Can, take a step way back. Here's what I hear him saying, "I don't have any details." And he doesn't. The point of your communication was not to present an offer, but to open a door to a discussion in which you wanted to hear his point of view. Don't fall into the trap of assuming he's challenging you. You know you were never intending to have him give you all the equity (but he doesn't yet know that). You know it doesn't make sense for him to think he can come play daddy in the house on visits but apparently he has not figured that out (in the call if he brings it up you just say how do you see that working, you know I have to rent out the rental to be able to afford the mortgage, and then tell him you have to give it some thought to whatever he says--no need to commit to anything in the moment). This is just the first time he is faced with the not fun consequences of his choices and a little panic has set in. But don't take this to a bad place by responding to things he has not raised or being defensive. And you need to remind him that he started this discussion by saying the house had to be sold.
"Hey 00, thanks for responding. Yes, I didn't mention details because there aren't any yet. I'm just trying to set up a call to discuss the house since you brought it up in your email on ___________ and letting you know that I would like to find a way to buy out your interest so D4 and I can stay here. Of course I would like for us both to share our points of view and concerns and reach a resolution that would work for all of us."
