YOU SAID:
I am not sure if the other person is there or not
INTO JAPANESE
私は他の人がそこにいるかどうかわからない
BACK INTO ENGLISH
I do not know if anyone else is there
INTO JAPANESE
他に誰かがいるかどうかわからない
BACK INTO ENGLISH
I do not know if anyone else is there
You've done this before, haven't you.