Unfortunetly if you damaged anything it probably wont be visible until you shoot the bow some more. Alot of todays bows that are dry fired will quickly yield cracked limbs or cracks starting in the yoke or from around the holes containing the axles. I would be safe and at least replace the axles. If they are bent ever so slightly you wont notice it while shooting but they will wear your cams and eventually lead to bigger problems in short order.

As for the fraying, that is simply broken or unravling fibers on your string/cables and the only solution for that is a replacement. Personally, I hold ANYONE who dry fires the bows financially responsible. I would make your brother pay for the axles and new string. If it requires new limbs or had the bow exploded, I woulda gotten a new one with his wallet!

That's the breaks when being stupid!
RA