1996 Chevy Lumina Water in Oil

When I first bought the car several years ago, it was overheating. When I took it to the shop, there was water in the oil. The mechanic thought it was the head gasket. But, the repair wound up being something a lot less expensive / difficult to repair - some type of plug, I think.

The car has the same problem again. It was overheating. By this time, my oldest daughter had bought a new car, so I parked the lumina for a couple of years. Younger daughter is now 16, so trying to get it running again. My uncle checked the car. The oil looked ok, it wasn't overheating. My ex-husband has been working on it -- flushed the radiator, changed the oil, replaced upper & lower radiator hoses, etc. He changed the oil 3 days ago. It now has water in the oil.

A friend said that there are freeze plugs between the motor and the oil pan and that could be what is causing the water to get in the oil. There is a lot of disassembly in dropping the oil pan, so I've been trying to verify this information before we do anything else.

Is this information correct? If so, what is the best way to determine if it's the freeze plug or the head gasket?

Ex said that there are 2 cylinders that have low compression.

Thank you.