Has the property been deeded to the trust?
Lots of people form trusts that broadly outline the items to be covered.
Check with counsel, to verify that even if they actually recorded a deed transferring title from themselves to the trust, your mortgage retains it's first lien position. That's what you care about, not whether they signed as individual's or trustees. And as I said above, normally the trust contains language that address continuity and priority of existing obligations and encumbrances. (I typed a few trusts in my tenure as a legal secretary.)