The way they treated Kevin was how you'd treat a child that was on the spectrum or suffered from mental illness, but it sounds like they turned a healthy child into an extremely spoiled, entitled jerk that truly believed that the world owed him just for existing and made him completely dependent.
if i was the judge i'd fine the parents the 50k for the clear signs of abuse and harassment of suing their child and award op 50k in damages plus the court costs
And the parents are actually peeved that they didn't manage to properly parentify their other, USEFUL, son. They're going to die with no money because they gave it all to the worthless one, and wonder why the useful one wants nothing to do with them.