Grow up guys and gals!
I don't know why I get a kick out of these two groups? Kind of like two seven year olds fighting in the back seat. And one of them yells, Mommy he's on my side! And the other yells, she hit me!
The two cerificates under FAR 121/119 each require appointed and approved management positions. Such as a Director of Operation, Director of Maintenance, Chief Pilot, etc... There is no reason why John Jones could not be the DO for "A" and "B" airline and the same for the other approved positions. All the manuals could be the same maybe even having both logo/company names on the header of each page. The aircrews could also all come from the same group or for that matter a third crew providing company. No where in the FAR's does it direct an airline to even have a seniority list. It is as simple as each seat must be trained for that seat.
The reason for maintaining two certificates has more to do with route awards than anything else and maybe brand idenity.
The longer the two groups keep throwing rocks at each others window, the long it will take to have a cohesive group. Grow up guys and gals and you both will be way ahead at the end of the day.