This is unreasonable. I’m guessing you’re Asian based on some of your other posts and in our culture (I’m also Asian) it’s normal to help support your SO’s parents if you are married and they are ailing. But it is something you discuss and budget together. You don’t just take the other person’s money.

NTA. If you’re already sending him 1/3 of your earnings that’s enough. Cancel that card. Also, talk to his parents. Do it in the “Future Mom and Dad I’m so sorry I don’t have any more money to give you. I’m already sending everything that I’m not using for food, rent, and tuition.” And see how they react. If they don’t at least do the fake contrition thing of calling themselves and their sons useless for not being able to support themselves you need to run because something is up.