mantuvierais

Verb

form-of imperfect plural second-person subjunctive

mantenerの二人称複数未完了接続法

English Meaning

second-person plural imperfect subjunctive of mantener

Si mantuvierais la calma durante la tormenta, todos estaríais a salvo.

もし嵐の間に落ち着きを保っていたなら、みんな安全だったでしょう。

If you had maintained calm during the storm, everyone would be safe.