Garnishing wages, attacking bank accounts, and foreclosing on real estate are all used to force payment to affected children.
Fannie Mae and affiliate mortgage lenders attempt to avoid foreclosing on homes whenever possible because it is a costly process.
The seller could be the owner, a trustee or the foreclosing lender.
The process of foreclosing on a home is a costly one for everyone involved, so in some cases it's financially better for the lender to work with the borrower and offer a modification or full refinance.
Also keep in mind that despite the hefty costs associated with foreclosing on a home, some lenders simply aren't willing to work with borrowers.