D.B.
Yikes. Sounds like a mess.
I can see that your older kids might be wanting to stay in the area, and they are intrigued by a father who disappeared but now seems to want to have some relationship. A male role model is important to boys, and you won't "win" if you are perceived to be getting in the way of that. I can't believe they will be happy living with him and all those people, but I also see that you can't hold out and maybe get a 2 bedroom, maybe a 4 bedroom.
It seems to me that your boys need to decide if they are "minors" and want a bedroom provided by Mom, or if they want to be on their own. If they are staying with you, then you have every right to make them do stuff to pack and get the house ready. That means you take away their cars or cell phones or computers unless and until they function as responsible members of the family. If they are, on the other hand, "adults" and beyond your right to dictate to, then they need to pack up their stuff and move to their own place. That can be with Dad, or they can get jobs and get their own apartment (wait until they find out how much money they have to put down, and that's assuming they can find anyone willing to rent to 18 and 20 year olds). So I'd send them out to look for a new residence and get some lease agreements so they know what's in store. Or they should start moving things to their father's place.
If they aren't including you in their plans or their thoughts, then you tell them you are making plans without them, you understand they want to stay in the area with their friends or to have a relationship with their father. You tell them you love them enough to let them go even though you will miss them terribly, and you hope they find good jobs and will come see you at Thanksgiving, you'll have a couple of inflatable mattresses or a pull-out couch for them and you will love to see them.
If you get a 2 bedroom in CA and then they call and say "we want to come home to you," you have to be tough enough to say "I'm sorry, there's no room for you here, because I made plans based on your desires and needs. But I will give you the names of some realtors and you can look for a place together or find roommates.
So they can't have it both ways - they are either kids and they don't decide, or they are adults and you don't bail them out.
Make a time by when stuff has to be out of the house, even if it means you get a storage unit. Tell them to rent one of those "PODS" (Personal On Demand Storage, I think), and everything they aren't using right now goes into that unit in the driveway or the yard - the house has to be decluttered to be sold. When you leave for CA, then they can pay to have the whole unit moved to their father's house.
I'd suggest you put something in writing, like a family contract, and have them sign it.
But you cannot be the person in charge of everyone's comfort, emotional well-being, housework, packing and so on. If they have adult privileges from you (allowances, cars, phones, etc.) then they are adults. Start putting things in their names so they get the bills.
Good luck!