how to know if you've unlocked all bros?

[Qvoth]

how do i know when i've unlocked everyone?

[Goose]

where it normally says x bros till unlock it will say thank you for playing

[Reverendo Bizarro]

If in the "Area Liberated" screen instead of "x rescues until the next unlock" it says "Thank you for preordering! You rule!", then congrats, you got all the characters.

Alternatively, if you have unlocked the Broniversal Soldier, you have all the characters, since he is the last unlock (though tomorrow or during the weekend there will be an update, so there will be more unlocks)