Question about hooking up two generators in parallel
So you situation when connected to the grid is that you have power from the utility coming in on Black-White-Red.  Loads at position (a) see 120VAC.  Loads at position (b) see 120VAC.  Loads at position (c) see 240VAC.  Phases stay aligned due to the transformer generating the voltages.  All is good.



Then you want to switch to generators.  



The leads from the 2 generators are Black-White and Black-White.  Connect the White's together and the Black's to Red and Black as shown.  Loads at position (a) see 120VAC.  Loads at position (b) see 120VAC.  Loads at position (c) see a voltage that is constantly cycling between 0 and 240VAC.  The 2 generators are not at the exact same frequency. So as they slip the sum of the two generators will be cycling between in-phase and 180° out of phase.  This may be harmful to some loads.

So in summary.  It's close.  But bad.  Don't do it.  Sell those 2 120VAC generators and get one that generates 120/240.