Meanings
Usage patterns
一人になるto become alone; to be left by oneself
The kids moved out, and I was left alone at home.
一人も〈動詞〉ないnot even a single person (does something)
There isn't even a single student in this classroom.
一人しか〈動詞〉ないonly one person (does something)
Only one person came to this party.