I sometimes sit beside my brother and watch TV while he's eating breakfast in the morning.
I put a blanket beside my brother while he was sleeping.
ーI sometimes sit beside my brother and watch TV while he's eating breakfast in the morning.
「時々朝、弟が朝食を食べる横で座ってテレビを見る」
to sit beside my brother and watch TV while he's eating breakfast で「弟が朝食を食べる横で座ってテレビを見る」
ーI put a blanket beside my brother while he was sleeping.
「弟が寝ている横に毛布を置いた」
beside my brother while he was sleeping「弟が寝ている横に」
ご参考まで!