Did you know them before, or did you meet them after coming/arriving?
ご質問ありがとうございます。
「知り合い」はacquaintanceですので、「もともと知り合いだった？」はwere they an acquaintance from beforeとwere they a prior acquaintanceに訳せますが、Did you know the beforeの方がいいやすいかなぁと思っていますね。
「来てから」はafter comingかafter arrivingかどっちでも使えます。
ご参考になれば幸いです。
Did you become friends since you moved there or were you friends from before?
Did you get to know each other once you moved into the neighbourhood or did you already know one another?
この場合、次のような言い方ができますよ。
ーDid you become friends since you moved there or were you friends from before?
「そこに引っ越してから友達になったの？それとも前から友達だったの？」
ーDid you get to know each other once you moved into the neighbourhood or did you already know one another?
「その近所に引っ越してから知り合ったの？それともすでに知り合いだったの？」
ご参考まで！
アメリカ合衆国 
カナダ 
