Two of the brides, were 13 and 15, old enough to understand what was happening.

这句话，断句有问题。第一个逗号多余，应去掉！

主语和谓语是两个紧密相关的成分，中间若没有其他成分插入，是不能随便加逗号停顿的。原句改为：

Two of the brides were 13 and 15, old enough to understand what was happening.

成分分析：

Two of the brides（主语） were （系动词）13 and 15（表语）, old enough to understand what was happening.（形容词短语作结果状语）

如果，在主谓之间插入了成分，则在该成分两端分别加逗号。例如：

Two of the brides, aged 13 and 15, were old enough to understand what was happening.