How to proof that marriage is a fake?

Sir meri girl friend ki shadi 4 saal pehle hui thi Uske 1 saal k bad hi uske husband ki death car accident me ho gayi.wo uske sasural me uske husband k bade bhai,bade bhai k 2 bachche jise usne bachpan se pala h aur uski saas k sath rehti h.husband k bade bhai ki wife ki b 3 saal pehle bimari se death ho gayi thi.ab problem ye h ki husband k bade bhai ne sare document jaise bachcho k birth certificate, aadhar card, voter id, bank pass book me meri friend ko wife dikha rakha h wo b bina kisi document pr sign kiye.unke beech me shadi b nahi hui h. marriage certificate nahi bana h bt ab agr wo chahe to ye proof kr sakta h ki meri friend uski wife h.hum kaise proof kare ki ye uski wife nahi h.kyonki use aadmi ne iske husband ki death certificate b nahi banbaya, na hi aisa koi proof choda h jisse hum proof kr sake ki ye uski wife nahi h.usne shadi k album, marriage certificate sb ko jala diya h...plz koi solution bataiye...