The whole idea of requiring at least a year of residency in a state to get instate tuition is to avoid those who move just for the purpose of paying less for public colleges. Different states have different rules, and as I understand it from CC, schools within a state may also be more/less strict. Owning property without that being your primary residence does not work anywhere (Illinois residents own vacation places in Wisconsin, but sorry, that doesn’t count- no matter how expensive and how much you pay in real estate taxes).
Plan your move for where you want to live and work. Every place has pros and cons. Do not move to a state presuming your younger child will get accepted to the state school of choice! Stay overseas if that is where you see yourselves five years from now. There are reasons you chose to move years ago and it worked for you. Trying to pay instate tuition is NOT the reason to move to a state and disrupt your entire lifestyle.