Your question contains a number of issues which are difficult to respond to in this manner. Feel free to contact me directly through my site if you would like to discuss this further. Generally speaking, a felon may not "possess" a firearm. Thus, the key is whether your son "possessed" the guns. Possession is not the same as "ownership". A person may "possess" something even if they do not own it. If your son knew about the presence of the guns and had the ability to access them and do with them as he wished, then he may have a very serious problem. There could, however, be legal avenues to challenge the entry into the residence and subsequent seizure of the guns. A successful challenge could lead to suppression of the evidence and possible dismissal of the charges. I hope this helps.
Hi. Yes, you are correct. I do have quite a bit of experience with federal firearms cases, as you may have seen from my website, etc. In short, a felon in possession of a firearm is a federal offense. However, there are various issues to be explored and litigated, i.e. whether your son was indeed in possession of the firearm (possession can be actual or constructive), whether the possession (if there even was possession on his part) was knowing, etc. If you and/or your son would like to discuss this further or consult with me about his case, please feel free to contact me.
(Please note that this information does not constitute legal advice nor does it establish an attorney-client relationship.)