YOU SAID:

no ones was in school like only 3 people

INTO JAPANESE

学校に3人しかいない人はいませんでした

BACK INTO ENGLISH

No one in school had only three

INTO JAPANESE

学校の誰も3人しかいなかった

BACK INTO ENGLISH

There were only three at school

INTO JAPANESE

学校には3人しかいませんでした

BACK INTO ENGLISH

There were only three people in school

INTO JAPANESE

学校には3人しかいませんでした

BACK INTO ENGLISH

There were only three people in school