Form W-4P for survivor pension and tax filing requirements for a disabled adult

My brother is a disabled adult child with ~$16,200/year of SSDI and no other income. He started living in a group home January 2025; thus nobody will claim him as a dependent any longer.

Because of his disability, he is newly eligible for a small survivor continuance annuity payment from my mom's California school pension. This should be under $6000/year paid monthly for the rest of his life.  CalPers has issued him a W-4P to fill out.

1. Given this adjusted income picture, should we fill out the W-4P to indicate "no withholding" or something else?
2. Given this adjusted income picture, does he have to file a Federal or CA State tax return going forward?

Thanks much!