As much as you probably don't want to hear it, it looks like neglect to me. That animal should not have been left like that for however long it's been going on. Injuries and things happen, but that animal should have seen a vet long ago. And had you not come home from school (I'm assuming your school is shut down indefinitely?) when you did it may have been too late.
Good luck with the vet appt. I hope you can get him back on track before heading back to school.
And for the animals sake, I'd be finding someone new to care for the snake while you're gone...or unfortunately re-home him. Leaving him in the condition he's in is unfair. Your parents clearly don't have the animals best interest at heart, and he deserves better.