Wow. Yikes. It sounds like you're confused and feeling attacked by your son and getting close to being completely overwhelmed...
I think that keeping your joy is an excellent goal, and one which is within reach, through a small shift in perception. From the outside, this appears to be a conflict of opinion, that seems to escalate into 'who has the most logical argument for/against'.
As you have experienced, this isn't a helpful place to stand, and unless you have some means of force, you cannot stop your son from disagreeing with you. In fact, if you thought about it for a while, I'm sure you'd feel that making him agree with you is just about the last on your list of goals for him and his future.
Now, from the inside-- the inside of you and the inside of your son-- you have a completely different perspective available to you. You know that you are freaked out by his response, and feel he's criticising you and your husband, and 'siding' with your inlaws -- a kind of betrayal, yeah?
But what do you think is happening from inside of him? While it's certainly not possible for me to determine that from *here*, I can make a few guesses based on his reactions, which might be more... generous towards him than the arguing has been.
I think he has a valid concern (and I think your inlaws do, too) -- which is not to say I think you need to change your decisions at all. This is where the third option comes in: there is 'with me or against me' and then there is 'how 'bout we all work together'. You need to hear and understand his concerns from his perspective in order to be able to address them effectively (and it still doesn't mean signing up for him to decide for your whole family).
By 'hear and understand' I mean that you need to be able to say back to him, in your own words, 'you are concerned that we will be homeless... which means to you that you won't have a safe place to sleep that is private and your own, is that correct?'
Now, with enormous restraint and diligent care, from that statement (when he agrees or disagrees that this is his concern) your job is to NOT try to explain why that's not a valid concern, why it's not likely, why it's wrong or inaccurate or anything else. Your task is to simply hear him with genuine concern and respect.
*When* your son feels completely heard, he will cease to need to repeat the complaint. If it comes up again, it's code for 'I'm concerned about this other thing, too,' and your task will again be to hear what he is concerned about.
The thing is, no matter how logical your plan or diligent your preparations or even if you decide to stay, you don't get to control the future -- and addressing concerns about what *might* happen is part of life. Yes, he's right -- you may end up homeless. You may if you stay where you are, too. There are no guarantees and we can only do what we can do, what feels and seems right at the time, with all the best information we can lay our hands on.
Being freaked out about the future is pretty much what 16yos are all about. If it wasn't this, it would be something else -- so don't take the fact that you've decided to move your family as the cause of his distress.
In a way, your husband is right: you have to stop arguing with him in order to stop arguing with him about it. Just stopping isn't satisfying to anything, though, and certainly won't lead to less conflict or more joy. Connecting effectively with your son, through honouring and respecting his concerns, will happily do both: less conflict, more joy.