"Four knives" in Engpsh can be said as "four knives". The phrase "four knives" is a straightforward translation of the Chinese phrase "四把小刀" and does not have any specific idiomatic or colloquial meaning.
Examples:
"He had four knives in his pocket."
"She bought four knives for her kitchen."
"The chef used four knives to prepare the meal."
Translation:
"他口袋里有四把小刀。"
"她为她的厨房买了四把小刀。"
"厨师用四把小刀准备饭菜。"