Beware of youtube videos about connecting 2 compressors together

I think part of the problem comes from the type of pressure switch and unloader. There are three or 4 types of unloaders that I know of, maybe more.

1...Head realease via the pressure switch. This is popular in the smaller compressors up through 2hp and has a separate tube from the pressure switch to the head. When the switch opens, the switch opens a valve in the switch assembly and drains the head

2..."Load genie" or other names. This one is incorporated into the check valve from the compressor to the tank, and when the compressor stops, the pressure is equalized between compressor and tank. This causes the "load genie' to shuttle, and opens a bleed hole in the load genie, draining the head. There are no other lines or attachments. One tube from compressor to load genie, screwed right into the tank

3....Mechanical release at the compressor. This is some sort of mechanical linkage right on/ in the compressor and causes the head release valve (unloader) to open when the compressor stops rotating.

4...Forget the name.........gasoline........There is a type of control meant for gas engines. They have a piston or other device to operate the governor, and idle down the engine when pressure is met, and an unloader device similar to a load genie.

No two ways around it you are going to have to have a pair of check valves to isolate the two compressors from whatever comes after, whether the check valves are part of the unloader system "or what"