From this I believe they are considered residents https://www.tax.virginia.gov/residency-status#:~:text=Resident%20--%20A%20person%20who%20lives%20in%....

From the instructions, my guess is that they would be required to file, but they would get a credit for taxes paid to VA  on their CA return and not owe any additional tax, since I expect CA to be the  larger.  tax https://www.tax.virginia.gov/sites/default/files/vatax-pdf/2020-form-760-instructions.pdf  If 

You need to determine their Virginia AGI - go through the instructions, or if you can do a demo VA return with the data, then PS can help you to determine the answer.