If it’s for two, we also have a double room available.
We also have a double room which two people can share.
❶If it’s for two, we also have a double room available.
(二人用なら、ダブルルームも空いてますよ)。
❷We also have a double room which two people can share.
(二人の人がシェアできるダブルルームもありますよ)。〜と言えます。
例えば: I see that you made a reservation for two. If it’s for two, we also have a double room available. Would you like to reserve that? (二人分の予約をしましたね。もし二人用なら、ダブルルームも空いてますよ。そちらを予約しますか?) 〜と言えるかもしれませんね。