Legal Question in Real Estate Law in California

There are a couple of issues here. The first is whether the father-in-law can kick you out now, while he is alive. Another is whether the promise to bequeath the house to you is enforceable. So far, it hasn't been broken, and it may not be ripe for addressing in court at this time. Has he now said he intends not to give his son the house, in addition to saying he wants to move in?

The answer to the first question (taking possession of the house) is probably yes, he can do that, but that is a lot less certain if, in addition to promising to bequeath the house, he has also made promises stating or implying that you can remain in it as part of the bargain.

The answer to the second question, i.e., whether he has a legal duty to see to it that his son becomes the owner upon his eventual demise, may be somewhat easier. There is a principle in law (actually, an equitable principle) called "promissory estoppel." The basic idea is that if X has made a promise to Y, and Y has relied upon the promise to his detriment, then X is "estopped" to assert certain defenses to an action to enforce the promise, including the requirement of consideration and the requirement of a written agreement.

In California, a leading case on this principle has facts somewhat similar to yours. You should look up and read the California Supreme Court's decision in Monarco v. Lo Greco (1950) 35 Cal.2d 621. Just putting the parties' names into a Google search will lead you to the case text and many articles discussing the principles involved in this landmark case.

In addition to whether the Monarco v. Lo Greco principles govern your situation, you'll have to get a lawyer to consult with you (based on more facts than given here) about his desire to move in now, and whether any of this is ripe for trial now or you have to wait until he passes away and see if the promise were kept.

You as a family could perhaps have avoided this situation by setting up some kind of family plan years ago, maybe using an irrevocable trust to hold ownership to the house, or in some other way protect your investment in mortgage expenses, etc. and his interest, if any, in having shelter in his old age.