Is it tax fraud and forgery?

My boyfriends brother is married but has been split for about 10 months from his wife, both living in separate states. She filed a joint tax return for them and it was agreed they'd split whatever the amount was they were to receive back however she would not give him his paperwork (said her computer had a virus) and then said she had to pay both state and federal taxes and there was no money. She is a gold digger and never worked, only had taken a tax preparation cl when they were together which was only a year, he had worked the entire time. If she did get money back, wouldn't both of them have to sign the tax return checks? What can he do? Thanks.