In Florida, a Seller is obligated to disclose to a Buyer all
known facts that materially affect the value of the property
being sold and that are not readily observable.

It appears that the sellers *did* disclose the pertinent facts
in this case, before the closing. Unless your friends can
prove that there were other pertinent facts known to the
sellers that they did not disclose, they have no legal grounds
to reverse the sale. It sounds to me like they didn't do
their homework and they're paying the price for it.

I'm curious what kind of contract binds them from selling the
house for three years; that's not typical in the home sale
contracts I've seen. Who, exactly, is prohibiting them from
selling the house?