Legal Question in Wills and Trusts in California

That depends on the contents of the trust document. The controlling law is Probate Code 16061.7, and much depends on whether the trust is now irrevocable.

If the trust became irrevocable upon the passing of your brother, then the children are entitled to a copy of the trust document. They may wish to retain counsel to enforce their rights here.

Note also that this answer assumes the trust is governed by California law.

I say yes, given what you have provided and the terms of Probate Code section 16061.7.

I agree. She should, in general, be providing a notice of the right to obtain a copy of the trust. You likely need to engage counsel to send her a letter.