I agree with Dongfang Xiaolai that there are very few six-character idioms and it is actually difficult to match the surname and generation. Moreover, many six-character idioms tend to be colloquial, and one word may not necessarily sound loud when used. In addition, there are two identical characters in many six-character idioms. Wouldn't it mean that there are two brothers with the same name?
Since there are six brothers, my suggestion is that it is very suitable to use the sentence from "The Great Learning": "In ancient times, if you want to manifest virtue in the world, you must first govern your country; if you want to govern your country, you must first regulate your family. "If you want to straighten your family, you must first cultivate your body; if you want to cultivate your body, you must first rectify your heart; if you want to rectify your heart, you must first be sincere in your intention; if you want to be sincere in your intention, you must first understand it"
Everyone is familiar with the saying "cultivation, family management, country governance, and world peace" derived from it
Taking six words from it, the six brothers were named Zhang Xiancheng respectively
, Zhang Xianzheng, Zhang Xianxiu, Zhang Xianqi, Zhang Xianzhi, Zhang Xianping
Hope it can help you