Welcome, jaylee! Don't be freaked if your son is dx'd BP. It is what it is.

Whether your sister is BP or no... have to say, those symptoms sound nothing at all like untreated BP (I was dx'd about 15 years into it, even with clear cut symptoms, soo... have some "mileage" in the untreated catagory).
As far as the sister, it may be something strictly medical, but it may also be an ED thing (couple decades ago had a roomate who was anorexic... what you describe--as in eating causing pain-- is the closest to anything you've described and I've experienced at close proximity..I may be way off there, but...)