Majority have at least one parent who is Japanese.
"ほとんどは両親のどちらかが日本人です"
- Majority have at least one parent who is Japanese.
- Most of them have one Japanese parent.
- Most have one or both parents who are Japanese.
私はアメリカにある補習校で日本語を教えています。そこに通っている子供たちは、両親のどちらかが日本人か両親2人とも日本人の人達です。
- I teach Japanese at a supplementary school in America. The children who attend there have either one Japanese parent or both parents are Japanese.
- I teach Japanese at a supplementary school in the US. The children who attend the school have either one Japanese parent or both parents who are Japanese.
The great majority of the students have at least one parent who is Japanese.
ご質問ありがとうございます。
この場合、補習校で通っている子供に関して、「ほとんどは[両親](https://eikaiwa.dmm.com/uknow/questions/34087/)のどちらかが日本人です」と言いたいなら、英語で「The great majority of the students have at least one parent who is Japanese.」と言えます。
ご参考になれば幸いです。
Most of the kids who go to that school have one parent who is Japanese and sometimes both of them are Japanese.
この場合、次のような言い方ができます。
ーMost of the kids who go to that school have one parent who is Japanese and sometimes both of them are Japanese.
「その学校に通う子供たちのほとんどは、片親が日本人か、両親とも日本人ということもあります」
most of the kids「ほとんどの子供たち」
to have one parent who is Japanese「日本人の親が一人いる」
ご参考まで！
アメリカ合衆国 
カナダ 
