Joint Trust vs. Separate Trust.

A married couple can set up a joint trust, which could be modified even after a spouse dies. 

They can also set up separate trust instead.   And when one dies, the dead spouse's trust could become a irrevocable trust and manged by the surviving spouse.  This way the property is managed but the dead spouse's trust cannot be modified. 

Exactly which type of trust is suitable for you is hard to say.  Younger couple might want separate trust because if one dies young the other might remarry.  An older couple might use a joint trust, even if the surviving spouse might remarry, chances are .... I am not going to speculate. 

This is why you need to talk to a lawyer instead.  Trust is a big topic.