You file the FAFSA with your mon’s Income and assets. She must include any child support and alimony.
Her primary residence is the house in MA
Since your parents filed jointly, your mother must separate out her info from your dad’s.
If your mom has part ownership in the California house then she must out that down as an asset
She does not have to put down the money in the retirement account (401k/403b) However she must put down any contributions she makes to the account
If she has a regular bank account she is using to save for her retirement, then that is an asset
I will let the California people talk about your eligibility for in-state at UC