Legal Question in Wills and Trusts in California

It is hard to answer based on your facts. It really depends on what the Trust says. The Trust may have separate and community property and designate specific items of property to specific people that may or may not be tied to the second spouse. If second spouse has use of the property until death and then distribution, A-B, that second spouse's share of the Trust can be given any way s/he wishes. As to the first to die spouse's share, yes that share becomes irrevocable on death. If survivor chooses to waive the right to use the property and pass it now, that can certainly be done. Whether by Satisfaction/ Waiver would depend on the circumstances in the estate but sure, it can be done.