determining stepped up basis for CA real estate

My parents own 3 houses in CA (one is their primary residence and 2 as rentals) which are held in a revocable living trust. My father died in Nov. and now my mother, as trustee and surviving spouse, would like to sell these properties and buy one new home.
We know that she can sell her primary home without claiming Capital Gains.
How do we determine the stepped up basis for the 2 rentals? Since CA is a community property state would the whole basis be stepped up, or just 1/2?

>>would the whole basis be stepped up, or just 1/2?<<

Only that portion which is subject to Federal Estate Tax.

How can there be Estate Taxes due on property held in a Living Trust? If she decides to sell property from this trust, which she (as the surviving spouse/trustee) is entitled to do, what part of the community property is subject to the stepped up basis regarding capital gains taxes? Thanks in Advance.

>>How can there be Estate Taxes due on property held in a Living Trust<<

I didn't write that ANY tax was DUE,...you are indeed confused.

You wrote that the property is in "...a revocable living trust..." The only way for that to happen is that your mother had to put her entire interest in there. Your father could not have done that,...he's dead.

Her interest is the 1/2 she owned, and the 1/2 which passed to her on death and was subject to Federal Estate Tax. The step-up is on the piece subject to Estate Tax, whether tax was due or not.