"让他们心情愉悦"可以用英文表达为 "make them feel happy/pleased/depghted"。
"Happy" 是形容词，表示 "快乐的"。
"Pleased" 是形容词，表示 "高兴的"。
"Depghted" 是形容词，表示 "高兴的"。
下面是一些例句：
I want to make my friends feel happy. (我想让我的朋友们心情愉悦。)
I'm glad to see you so pleased. (看到你这么高兴，我很高兴。)
She was depghted when she received the gift. (她收到礼物时非常高兴。)