A lawyer who represents himself has a fool for a client. You can extrapolate that maxim to lawyers representing their children. Here Gus and Jane Martin saw their son getting counseling and heard the racist tirade and decided to press the big red button. They should have had outside attorneys guiding their ship and not use their emotion to go nuclear. Now their son is caught in a firestorm when this whole issue could have been handled much better behind the scenes.
Their son has plenty of facts against him. Plenty. Starting with the very fact that he plays a sport that, by definition, is about bullying. Then go from there. The sincerity of Martin seems to be severely lacking as well. The locker room supports Incognito. Martin never told Tannehill, Philbin, and management of any issue. Martin himself hazed others. Martin texted Richie and said he didn't blame him. Martin played the tape in the locker room and laughed. Martin is 6'5 300 and may offend people who will think he can't be bullied at that size and his playing that card is an overreach that trivializes people actually bullied. His teammates almost universally support Richie and vouch for him while its clear Martin does not have that same respect. Hartline didn't want to answer whether he wanted Martin back. His character is not respected. Many, many jurors and Judges will see that.
Beyond all that, the damages Martin could get amount to rounding errors for the NFL. They can squash him like a feeble bug. Martin's earnings potential is far from certain. He ranks in the lower quartile of players. He is just as likely to be out of the league on the league average of 4 years as he is to get a decent contract next time he is up. As for emotional distress charges, he has a ton of facts against him.
Overall, if the Martins think this is an easy case for them, think again. Public opinion may be that Incognito was wrong but that doesn't mean he can get enough of a jury to sign off on Martin being right. He has a laundry list of facts going against him. And his parents used their parental emotion to go nuclear in a way that may have a poor outcome for Jonathan. Judges and juries may be a roll of the dice for the kid. It's going to be a struggle for him to get a court to sign off on his story.