It may be inferred that, for an agreement to have the effect of defeating creditors, there must have been creditors in existence at the time of the agreement or other transaction and it must be those very creditors who are defeated by a later shortfall. 

参考译文：可以推断，一份协议如果具备击垮债权人的效果，在订立该协议或处分该财产时，起码有这样的债权人存在，而该债权人为随後的财产流失而蒙受损失。

第1个it 为形式主语

第2个it 为强调句型结构it is +强调内容+that/who结构

It must be those very creditors who are defeated by a later shortfall.

根据主语=it，谓语=must be those very creditors.很显然主语和谓语不一致，因此不是“代词”作主语，而是强调句型"it"