When property is not divisible (likely applies to single family homes) it goes to public auction and is sold to the highest bidder. There's no option there.
Obviously, the other two siblings can pool resources and try to outbid the investors, but you would need cash to do it, and that might be problematic.
You can read the Florida partition statute at:
http://www.leg.state.f...
Partition lawsuits not only can result in a "fire sale" price for the property but likely generate a large amount of lawyer's fees.
As a matter of strategy, filing the partition lawsuit and serving it on sibling might make sibling more reasonable once the costs are revealed to him.
The opposite side of the coin is that the sibling may get ticked off enough to practice scorched earth warfare which results in the other 2/3 owners spending lots of money on lawyers and losing lots of money on sale.