While driving the car, we heard a pop from under the hood and then loud rattling on 1993 Toyota Land Cruiser

The noise got louder when we accelerated. We drove the car home slowly, and parked it. When we checked the sparkplugs, we found that one had detonated within the third socket, and it drove part of the sparkplug into the wire. We replaced all 6 spark plugs, as well as the plug wires. Just to play it safe, we vacuumed the cylinder to get any of the ceramic out. Started the car and the noise was still there. Checked the Haynes manual and it looks to be the pistons. Tried to start the car recently to have someone hear it and now it won't start at all. Do you think it could be the piston springs? There has to be a reason for the spark plug to detonate. Prior to all this, we had to replace our radiator and hoses as the radiator cracked in the upper tank. That was replaced along with the thermostat to play it safe.

Asked by for the 1993 Toyota Land Cruiser
In my opinion, it sounds like the piston rod pin that secures the piston head to the rod cracked allowing the piston just enough slack to impact the spark plug. You probably knocked a hole in the piston. Likewise with debris inside the combustion chamber while driving you've scored up the cylinder wall and destroyed the compression ring.

Pull the oil pan and look for piston material, remains of the spark plug and metal fillings.