They all have a component 四 and have the same pronunciation as that of 四 sì
君子一言, 驷马难追。jūn zǐ yī yán, sì mǎ nán zhuī. A real man never goes back on his words/Even four horses can not take back what one has said.
泗, 驷, 柶 and 牭 are all pronounced sì.
泗 mostly appears in 泗水, a name of river in China. 驷 means a team of four horses and mainly appears in this expression “君子一言, 驷马难追.”