If you move during 2021, for tax year 2021 you'll file as part-year resident in each of the two states.
If you're a W2 employee, your remote work earnings are not taxable by CA until you become a CA resident. CA does not tax non-resident remote W2 workers. Your earnings remain fully taxable by MA until you establish CA residency. So you should withhold for MA prior to your move, and CA after.
CA requires that you use the same filing status on your CA return that you use on your federal return (there is an exception for military). CA is a community income state. That means that your income for CA tax purposes after you become a CA resident will be split equally between you and your wife, and will be considered CA-source income. You can request the CA part-year resident tax return instruction booklet here:
https://www.ftb.ca.gov/forms/Search/Home/FormRequest/4311
You become a CA resident for tax purposes when you begin living in your new permanent home in CA.
**Answers are correct to the best of my ability but do not constitute tax or legal advice.
