We would be able to reserve a time for both of you, but at different times.
I'm afraid we can't give both of you the same time slot, but if you could come in at different times, we could make an appointment.
ご質問ありがとうございます。
予約を承る側が使うフレーズとして訳しました。
① "We would be able to reserve a time for both of you,"＝「お二人のご予約は取れますが」
"but at different times."＝「ただ、違う時間帯でしたら。」
② "I'm afraid we can't give both of you the same time slot,"＝「同じ時間帯はお二人では難しいのですが」
"but if you could come in at different times,"＝「でも違う時間帯に来ていただけたら」
"we could make an appointment."＝「ご予約は承れます。」
ご参考に。
アメリカ合衆国 
