But wait a minute, if the guy in Colorado already owns the guns, i.e. is the registered owner, then there is no requirement to have them re-registered to himself. The Dad is not selling them to the Son, the Son is only getting his property shipped to himself.

I would prepay the UPS here and send the shipping labels back east, package them for shipment, affix the prepaid label and drop them off at UPS, or better yet have them come and pick them up.