Couplets are mainly about playing with textual techniques, and there is generally no need to worry about semantics.
"The willow pavilion and the evening green" come from a poem by Liu Deren, a poet of the Tang Dynasty, but I don't know the specific work.
"Hibiscus Curtain Fan Autumn Red" comes from "Heqiao Tower Fu De Qun Gong's Night Banquet" by Tang Dynasty poet Tan Yongzhi.
It is said that Zhao Zhiqian (a calligrapher and painter of the Qing Dynasty) collected sentences into couplets.