Wells is one of the editors who always (take,takes) a leadin

Wells is one of the editors who always (take,takes) a leading role in (his,their) community
这题到底是选单数还是复数?语法教程的答案书上说takes/his 或take/their都可以并且是Informal的用法我非常不理解.我认为第一个应该是takes.