@Karen_pdx But Mom did not retain a life estate.  When we have a paucity of facts, let's not make up too many of our own.  Since when does a trust not allow co-trustees any legal right to participate in management decisions, the way an LLC can?  And they can manufacture a "discount" based on not having 100% ownership of an LLC, but they can manufacture the same discount for sharing ownership with a sibling.  

And, ancillary probate can be avoided just as easily with a trust as with an LLC.  

I wonder if Mom paid capital gains tax on the arm's-length selling price.  Or maybe Dad just died and she has stepped-up basis.  Which now decreases every year that the kids are claiming depreciation.  It's like paying income tax on their inheritance.