Not Canon btw
Just got a small Headcanon of how they met each other based on the toons so prepare to show my cringe talks:
I know Red and Terence(somewhere hidden) are first cuz it also known for "Red's flock" or smthing²×
Second is Matilda since she's the first flock Red, Then Bomb who thinks stealing one of the egg would keep him safe but got caught by Matilda, so he grew up under her care and lectures.
4 years later is Chuck who was lost in the forest and surviving on his own until his fear came true: strong thunderstorm/heavy weather which scares him and in vulnerable state. Thankfully, he was found by Matilda and retreat to the flock area where the other birds are. Chuck is not used to this place and too quiet to talk, of course he was terrified from the heavy storm. Few months later, Chuck became better, gaining his speedy skills and being hyperactive. Of course Matilda has to watch over him or one wrong move could lead risky.
Year later, Chuck found a big egg out of nowhere, which is pretty unexpected for Red and the others.
Both Matilda and Chuck(I guess) took care of the big egg, while Bomb and Red handle the smaller ones. Few months later, the big one hatched and revealed to be baby blues(haha puns intended)