Moving from where?  Your name suggests Arizona.  Not that it matters, but there is a huge difference between how the two states tax part-year residents.  Arizona says, "we don't care how much income you made before you got here."  California says, "figure your tax on all of your income for the entire year, then if 10% of it came during your period of residence, pay us 10% of that total."  

Are they sure they are moving mid-December?  Domicile is physical presence and intent to stay.  Shouldn't they wait until after the holidays to decide if they really want to make the move permanent?