Even if Patrick is being a total dick nothing he has done is illegal. Winning a case of fraud by claiming you were too stupid to read what you signed is not going to be easy unless you can be proven to be mentally incompetent. Patrick's blackmail happened after the contract (loan agreement) was done, and people can withhold money they control from other people for any cause. Telling your daughter you don't like her girlfriend doesn't rise to the level of "domestic violence".
But let's establish that DPC is using this loan as a MacGuffin. US federal student loans don't work the way that Maya's is being portrayed. FAFSA loan money is obtained and disbursed through the school, not the student or the parent. The loan money is then applied to tuition, living expenses, fees, and other purposes allowed under the law (no, Quinn can't pay off her drug lord with hers and MC can't "borrow" from it to pay for hookers).
Also when someone cosigns a loan with you they don't get control of the assets; you do, but as the cosigner they are obligated to repay the money if you default. That's all there is to it.
However for the sake of argument let's say that Maya's loan is not a standard student loan but an unsecured loan (unlikely in the amount, but let's just pretend) in Maya's name with her dad as a cosigner since she doesn't have any credit history. Even then her dad doesn't control the money being paid out. Only if the loan was taken in his name, such as a second mortgage on his home, would he be able to control it, and Maya would not be cosigning with her dad on that since she doesn't have any credit. He might be able to control the loan money if Maya was declared legally incompetent, but then he'd still be on the hook to fully repay it plus any interest. If her dad took the money and bet it all on red in Las Vegas and lost it both his and Maya's credit would be ruined, not just hers. I don't think even Patrick is stupid enough to wreck his entire financial life over Maya wanting to go muff diving from time to time.