I've done it with industrial back up generators. Voltage and frequency have to be synchronized on all generators.
Don't know if you can do it with home generators.
yes. However... You will be limited to around 4200 watts before the 2000 trips out.
if it is an inverter generator, you can link them no matter the brand, I have paralleled honda, ryobi, yamaha and champion together with no issues.
I can run my 50A camper with one pair if I only need one AC, or I can link up two pair to feed 110v per leg at 25A and run the whole shebang.