You might consider changing the name of the shop.
店名の変更をお考えになってはどうでしょう
You might just as well leave now.
そろそろ出発されてもよろしいでしょう（◆may as wellより丁寧）
You must agree to repay the money to us [us the money].
借りた金を返すことに同意せよ
You must be in 8th grade or under to participate in the Kids Club.
子どもクラブへの参加は８年生以下が条件だ
You must be tired.
お疲れでしょう
You must come and have tea with us.
ぜひうちへお茶にいらっしゃい
You must get up at 5 a.m. so as to catch the first train.
一番列車に間に合うように午前５時に起きなくてはいけません
You must have finished your report by next March.
君は来年の３月までにレポートを仕上げなければならない．
You must keep your credit cards safe.
クレジットカードは安全に保管しなさい
You must know yourself.
人はおのれ自身を知らねばならない
