YOU SAID:

I was playing Fortnite with my friend while my sister was in my house

INTO JAPANESE

妹が家にいる間に友達とフォートナイトをしていました

BACK INTO ENGLISH

While my sister was at home, I was fortnight with my friends

INTO JAPANESE

妹が家にいる間、友達と二週間過ごしました

BACK INTO ENGLISH

I spent two weeks with my friend while my sister was at home

INTO JAPANESE

妹が家にいる間に友人と2週間過ごしました

BACK INTO ENGLISH

I spent two weeks with my friend while my sister was at home