Her parents owned it and willed it to the grandchildren in a generation skipping living trust. The estate only charges her $695 a month in a rent control building in SF. What happens to me when she dies? I’m the executor of the will. How long can I stay? I’m one of the grandchildren as well as executor.
Are you the trustee? Or are you just your mother’s executor? Is there a property manager?
Even as a beneficiary you should have been notified that you were entitled to a copy of the trust. You will almost certainly have to consult a lawyer, but try reading the trust first. What does it say about the building, the income from it, personal use by trustee or beneficiaries, or eventual sale and distribution of the proceeds?
As a resident, you would like to be an official tenant and be able to continue at the cheap rent. As a trustee, you have a duty to manage the property for the benefit of the beneficiaries. So you may need a lawyer that can address both sides and help you to navigate the conflict of interest.
San Francisco has unique laws, you may want to consult local sites like https://sftu.org/rent-control/https://sftu.org/rent-control/
You can't really ask your question here since this is a global forum and state-specific laws will impact your situation. Also because it is complex and we can't know all the details necessary. There are no consequences or accountability if someone here gives you an erroneous answer that you act upon. Consulting with local professionals will be well worth the investment.
Who is the trustee?
How many other grandchildren are there?
Are you being paid for caregiving?