The two brothers are as like as two peas.

as like as peas是习语,很相似的意思,不同的豌豆也都长得差不多嘛.可以用来比喻人,也可比喻物.
as+adj.+as是固定用法,和……一样,
如as tall as--和…一样高；
as famous as--和…一样著名
like在句中是形容词,就是说和两颗豌豆一样相像,难以分辨彼此