I wish they would have let people evacuate the airplane from which ever exits were available even though all four exits might not have been checked for safety first.
この場合、次のような言い方ができますよ。
ーI wish they would have let people evacuate the airplane from whichever exits were available even though all four exits might not have been checked for safety first.
「4つの非常口すべての安全がまず確認されていなくても、可能な非常口から飛行機から避難させてほしかった」
to let people evacuate「人々を避難させる」
to checked for safety「安全を確認する」
ご参考まで!