Well for me, the rich in-laws and ML are kinda dumb at this point.. I mean they have all of the money and haven't they heard of a thing called "investigation" and a "DNA Test"..
My theory is the dead Grandfather is probably the only sensible one who investigated the whole thing.. But he didn't bother telling the rest, cuz its probably and test of trust or something... I'm not sure.. I mean look at the kid, a carbon-copy of the ML..
Or maybe perhaps,
Someone set up FL and the other guy ,who they said that FL cheated with.. And it might have had been someone inside the family who orchestrated it and made it seem real so that the rest of the familia won't investigate..
Sorry, it kinda just came to mind..
The plot is predictable, but I still wanna see the people falsely accused her suffer with pain and regret.. Idk, it just gives me satisfaction(︶へ︶)