How best to paint a flag?

Ok, for sporting purposes I have envisioned buying two polyester flags in my team's colours (blue and gold), each 3x5 feet. My plan is to run a pole up each flag, then attack velcro so they can be joined together at the other end- in order to make a two-tone banner that can be hoisted before and after the game, and split into two flags during the game. I plan to use white paint on the royal or St.Patrick's blue side and dark blue paint on the gold side. Banner will read together 'WE ARE LEINSTER' (WE and LEIN on the blue side, ARE and STER on the gold). This could be amazing, or it could be a total flop.

Advice please from people who know stuff:

What kind of paint can I use that will not crack, but will be durable and flexible enough to allow the separated flags to fly?

Would you recommend or advise against painting both sides of the flags? (advantage being that when split, someone waving the single flag could still convey the full WE ARE LEINSTER message- disadvantage would be added weight and possible loss of flexibility depending on the paint).

Will this work?

Thanks a million!