[derpingtonmanth]

My grandfather told us today that he wants to marry some lady we've only met about a week ago (apparently some of the other members have known for about 3 months). I apologize because this will sound greedy, but please don't be like Yahoo answer and ignore the question: Since he is in his mid 80's we are concerned that if he were to die before she does, and even though there exists a trust for the family to what his assets will split into, what entitlement does she gain? Like, does she get to keep the house because of the marriage or what are the actual laws relating to this?

[Fr_Chuck]

This being an international site, where she is located makes a difference.

But yes he will gain some rights, and more in other locations. She needs a will. Has property or money already been moved into the trust, or is the trust merely to be funded from the estate.

[joypulv]

If he set up a revocable trust, he can change it.
If he set up an irrevocable trust, he can't.
If he has a will for all other assets, he can change it right up until his last breath.
If there is a trust, chances are there is a will.
If there is no will, then who gets what outside of the trust depends on what state he is in. But a wife usually gets at least half the house.
Tell us the state if you wish, or Google it's intestate laws.
If you suspect the woman's intentions, talk to an attorney.

[AK lawyer]

... what are the actual laws relating to this?

What is the actual state or country in which your grandfather lives?

He might want to consider a pre-nuptual agreement.

[ScottGem]

As Joy suggests, someone who has gone through the process of setting up a trust is likely to have a will. Unless he changes the will, his estate will be distributed according to the will.

He may also be able to change the trust if its not irrevocable.

So its impossible to answer your question without knowing where he lives, the terms of the trust, whether there is a will, and more.