How can two ppl be collecting so much SSI benefits?

my sister n law and fiance both collect SSI. He is bi polar. She has chronic fatigue. They said they are making at least 50, 000 dollars in disability. They also get food stamps, medicare, Heap and only pay half of taxes! My husband and i are furious that they are scamming the system. And to be honest, they dont at all seem disabled! They aren't married. Could they not be claiming something? Can you really get this much money from the government? Everyone else I know who has disability, cant even hardly afford to pay their rent, let alone 2 brand new 20,000 vehicles, a nice house (worth at least 100k). It doesn't seem to add up. Could this be right?