Someone who is eleven can be told how it is, can't he? Just make a decision and then put a positive spin on it to him. I know you're trying to make him happy, but otherwise he might feel pressure to make the "right" decision. That happened to a friend of mine as a child during his parents' marital problems and it was tough on him. Take it out of his hands. It is a favor to him.
You can respond to his text that you will need more time to think about it, can't you? You need somewhere to sleep. Is he gone totally crazy in his depression that he would have his children out on the street or on the sofa at grandparents? Is he just trying to bully you into selling? You may need to consult a lawyer about your rights.
If the 4-wheeler is just a recreational item, maybe just deal with that first because it is a smaller decision.
