R.M.
After 2 weeks of diarrhea I would definitely be in touch with the doctor for you son. I hope you are keeping his liquid intake up so he doesnt get dehydrated. As far as the stuffiness in the nose...get some ocean spray (or the generic for about 1/4 the price!!!) and use that to thin the secretion and make it easier to suction it out with a nasal syringe. Keep the fluid intake up to thin it out and maybe run a humidifier in the house.
For the adults you could use Mucinex or Mucinex D ( Talk with the pharmacist and see which he would suggest...depends upon your symptoms.) It helps to thin the mucuos, as long as you drink lots and LOTS of water to help it work!!! It really does work wonders....we sell TONS of it at the pharmacy where I work.
For the adults you could also get a Neil Med SInus rinse....it is a sodium solution that you use as a nasal rinse....it REALLY helps to clear out your nose and sinuses. I resisted using it for a long time because the very idea of it just simply grossed me out, but now I am a huge advocate of it!!! The ones that we have at our store are behind the pharmacy counter, but only because it is something that we order in seperately from the grocery store.
Good luck!!