Should we move in with the in-laws?

My in-laws have been living with my family, my wife, two year old son and I, for almost three years now. We've been crammed into a two bedroom apartment and it has pretty much reached a boiling point. They have offered to let us stay with them when they purchase their house. Hopefully within the next six months. All we've ever wanted was to buy our own home and raise our family in a nice neighborhood but this seems like a far off fantasy on one income in california. We've made the decision to move to oregon as soon as we can save up a down payment and a cushion. Should we take up the in-laws' offer and move in with them, saving almost $20,000 in a year, enough to make the jump to oregon, or get our own place when the lease is up in six months and save only about $10,000 over a year?