Honda says you can parallel a 2000i and a 2200i generator, so I doubt that's your problem. If both generators load up when you try to start the air conditioner the paralleling cable is OK.
More likely is the generators develop less engine power at high altitudes, so they will overload more easily than at sea level. Inverter generators have a hard and fast maximum power limit, they don't degrade gracefully like conventional generators when you approach their maximum power limit.
Engines lose about 3% of their power for every 1000 ft. above sea level, causing the generator's maximum output power to degrade a like amount. At 5200 ft. you've lost about 15% of your generator's low elevation capacity.
Make sure both generators have their Eco Mode switches turned off so the engines are running at full speed.
Other things that are on may demand part of the generator's output, reducing the amount of power it can send to the air conditioner to overcome it's starting surge. One item often looked is switching the refrigerator to Gas Mode to save the 300-400 watts used by it's electric heating element.
Higher temperatures also increase the amount of power needed to start an a/c.
If this doesn't help, you may have to get a hard starting capacitor for your a/c compressor to reduce it's starting surge.