have a good relationship with one's sibling

lose a sibling
きょうだいを亡くす

child without a sibling
《a ～》きょうだいのいない子ども

grow up with a sibling
きょうだいと一緒に育つ

have a good relationship with one's sibling
きょうだいとよい関係を保つ

They deal with jealousy, peer pressure and sibling rivalry.
彼らは嫉妬、仲間からのプレッシャー、そして兄弟内の抗争を扱っています。

Only children never had to compete with a sibling for their parents' love and attention.
一人っ子は親からの愛情や注目をきょうだいと競う必要がありません。