Marriage: We are accused of fraud marriage

This case has been ongoing for 3 years now. It all started when my stepdad was visited by 3 immigration agents at his door. They asked him a few questions such like why he was not living with my mom and me at my house. The reason was that he was always yelling at me and we decided to kick him off for a while. Since then they believe my parents have a fraudulent marriage. They denied my mom's permanent resident status. Why!? What proof do they have? Just because they knocked on his door and saw they werent living together that means its fraud? Ridiculous. We have most of the proof that it is NOT a fraud... my stepdad and my mom has a number of joint things such as bank accounts, credit cards, tax returns, photographs, evidence that my mom has made my stepdad a beneficiary on her life insurance and vice versa and records of countless hours on the phone. The only thing fact they have against us is that he is not living with us, BUT, he used to. This is extremely weird. Why are they so persitent on us? I mean 3 men showed up at my stepdads door saying his marriage is a fraud... i dont hear of this kind of things often. Also, from what i can interpret in one of their letters, they seem to claim to have been watching us and seen that my stepdad doesnt live with us. Thats ridiculous. Are they trying to "intimidate" us or something?

We have filed an appeal so i guess this will be taken up to a higher tribunal. Does anybody have any insight about this situation?