"There were other people to weigh in on their fight."
"There were people weighing in on their fight."
"There were other people to weigh in on their fight."
"there were ~" 「〜もいた」
"other people" 「他人」・「他の人」
"to weight in on ~" 「〜を仲裁する」
"their fight" 「彼らの喧嘩」
"fight" 「喧嘩」"argument" や quarrel" なども使えます。
"There were people weighing in on their fight."
"there were people ~" 「〜人もいた」
"weighing in on ~" 「〜を仲裁している」
[仲裁する](https://eikaiwa.dmm.com/uknow/questions/46432/)についてもっと詳しく知りたい方はクリックしてください。
There were some people who tried to break up their fight.
There were some people who tried to intervene when they were fighting.
この場合、次のような言い方ができますよ。
ーThere were some people who tried to break up their fight.
「彼らの喧嘩を仲裁しようとする人もいた」
to break up one's fight で「人の喧嘩をやめさせる」
ーThere were some people who tried to intervene when they were fighting.
「彼らが喧嘩をしている時、仲裁しようとする人もいた」
to weigh in は喧嘩をやめさせようとするのではなく、加勢するか、議論に加わることを意味するので、もし喧嘩をやめさせようとする目的で仲裁に入るなら、上の例文のように言うと良いでしょう。
ご参考まで！
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