Legal Question in Real Estate Law in California

That is such a vague question. Who is the "other person?" Who sold the house? Who was on title?

Excuse me??

you can't convey title to a buyer without all titleholders consenting and signing all the sale, escrow and title documents.

I will assume from your vague question that you mean there are co-owners of some sort. In such a case it is not illegal to sell the house without the other's consent, provided you disclose to the buyer that you are only selling the share of the house that you own. It is not so much illegal as simply impossible for you to sell the other co-owner's share. They have to sign a deed to the buyer or the buyer doesn't get their share.

You can sell what you own. You just can't sell what is owned by the other title holder. Most buyers do not want to buy only a portion of the property, and if they are willing, the price is usually drastically reduced.

On the other hand, if you are a co owner, you may be able to force sale of the entire property through a partition action.

"He who sells what isn't his'n, must buy it back or go to prison."