In these shops differences of rank were blurred as artisans and masters labored side by side in the same modest establishment, were usually members of the same guild and religious sect,lived in the same neighborhoods,and often had assumed(or real)kinship relationships. 

labor 这里是及物动词用法。labor sb. 的意思是“make sb. work”（使劳动/工作）。及物用法暗示人为地安排人们去劳动。过去分词 labored side by side in the same modest establishment 作 artisans and masters 的定语。

【翻译】在这些作坊里，等级的差别被模糊化了，因为在同一个简陋的场所并肩劳作的工匠和大师们，通常是同一行会和宗教派别的成员，住在同一个社区，而且往往认为有(或真正的)亲属关系。