There is right and wrong, then there's smart and stupid.
It may not be right that you can't hold illegal aliens for the police to arrest, but these people were definitely stupid for holding illegal aliens. If you are a U.S. citizen and don't think the government or some do-gooder group won't come after you for protecting yourself or your property, you are stupid.
I agree, the former owners were stupid. It's now time to make the present "owners" assume the "former" position. We can KNOW their names, court records will show that. We KNOW they're illegal - so where is the ICE detention? or have people been too "upset" to think rationally and seek the illegals' removal?