Does anyone know if I would be allowed to bring my power bank of 30,000mAH in my carry-on bag for all 3 three of these airlines?

The IATA passenger guidelines for lithium batteries for passengers are here.

Your powerbank has a capacity of 30000 mAh, which probably means 111000 mWh (based on the 3.7V nominal voltage of lithium batteries), or 111 Wh. Note if they don’t display their capacity in Wh (or mWh), most people would use the 5V output and count 150 Wh.

This means they exceed the 100 Wh limit which would allow you to carry them onboard without hassle. You are allowed to have 2 of those in your carry-on, but you need operator approval, which probably means you need to call them to secure that approval, if that’s even possible.

Note that those are only guidelines and individual airlines may deviate from them. You’ll have to check each airline’s dangerous goods regulations to see if they differ.

It’s probably much easier if you use 2 similar powerbanks with a 20000 mAh capacity.

There's a reason you see a lot of 26,800mAh power banks for sale--because that's the largest size you can carry on without getting special permission. Note that the power bank industry is a bit deceptive--the number is the capacity of the cells, not the power it will actually deliver to whatever ports it has. The voltage is being stepped up from the cell voltage to whatever it's being called upon to deliver.