You can also try to create an addition to the cage or a play area outside of it on the floor or a table. Before I learned about C&C cages, this was the direction I thought I would go in. It doesn't have to be made out of more panels if you don't have anymore, but something that he won't be able to destroy. If you put it against a wall or in a corner, you can use even less. Make sure the sides are sturdy by putting heavy objects against them or using zip ties if you can. Then line the area with shower curtains or towels. There's a lot you can do with this. If this is the only issue you're having with your parents (as in you're okay with maintaining food supplies, can keep it clean, etc), I would definitely try to keep him. If you feel that he would have a better home provided by a rescue (or knowledgeable animal shelter) than you could ever give him, you should give him away.
This sucks but it can often be hard for parents to fully realize the new pet they let their kid get does need more care and upkeep than they originally thought. On top of this, any unplanned financial constraints can really limit what they can do. See if this is something that you could get at a later date (ie in a few weeks) or ask if there's anything you can do that will get your pigs a larger cage (ie helping out more around the house; if you're old enough, getting a part-time job or just something that pays). Talk to your parents calmly and don't give up asking them for help (as in talking about it often). It might take a few more times before it either happens or is planned on.
In the meantime, let your pig out more often. Use towels or a thick blanket he can pee on to cover your bed for him to run around on. More laptime will really help him stretch his legs.
