"How many more people do we need to make two classes?"
"How many more people would make two classes?"
"How many more people do we need to make two classes?"
["how many more people" 「あと何人増えたら」](https://eikaiwa.dmm.com/uknow/questions/39364/)
"do we need" 「必要がある」
"to make two classes" 「ニクラスになるために」
"How many more people would make two classes?"
"would make two classes" 「〜でニクラスになりますが」
How many more students will we need before you make two classes?
What's the maximum number of students you'll take in one class?
この場合、次のような言い方ができますよ。
ーHow many more students will we need before you make two classes?
「２クラス作るには、あと何人の生徒が必要ですか？」
ーWhat's the maximum number of students you'll take in one class?
「１クラスの最大生徒数は何人ですか？」
こう言うことで何人に達したら、２クラスになるかがわかります。
ご参考まで！
オーストラリア 
カナダ 
