People hesitate to sit down beside someone who actually needs a courtesy seat on a train even though the seat next to them is empty.
この場合、次のような言い方ができますよ。
ーPeople hesitate to sit down beside someone who actually needs a courtesy seat on a train even though the seat next to them is empty.
「優先席に座っている人の横が空いていても、みんな電車で優先席が本当に必要な人の横に座るのを遠慮しがちだ」
a courtesy seat で「優先席」と言えます。
People hesitate to sit down beside someone who ... で「人々は…な人の横に座るのを遠慮しがちだ」
ご参考まで!