Legal Question in Wills and Trusts in California

It is not clear what you mean by put him in a trust. I cannot tell whether you mean transfer an asset to him, as trustee on her behalf, or just name him as a beneficiary to the trust, or some combination of the above.

Normally when property is transferred, and is subject to a deed of trust, it is either transferred subject to the deed of trust, or subject to the deed of trust coupled with an assumption. Please don't confuse the term deed of trust, with the trust that your mother in law wants to create. By deed of trust, I mean the instrument that the lender maintains a security interest in the home. All property transfers are subject to foreclosure for a recorded deed of trust, but a transfer with an assumption means that the transferee also assumes personal liability for the note, in addition to the risk of losing the property to foreclosure.

It is the personal liability on the underlying promissory note that affects a person's credit score, negatively when they get behind on the payments, and it triggers foreclosure. Simply being named as a beneficiary to an inter vivos trust alone would not damage his credit score.

A transfer by an obligor (mother in law) to an inter vivos trust in which she is a beneficiary (to that inter vivos trust) does not trigger or allow a lender to utilize a due on sale clause. (Civ. Code, sec. 2924.6 subd. (a)(4).)

It is not clear, however, whether your husband is to assume liability on the underlying promissory note, as an acting trustee, from the facts that you have provided. You would have to provide more detail, for me to give you a complete, definitive answer.