I suspect that thousand-year-old bones would be "new" to an archeologist. I don't think two years in storage would be a factor worth worrying about. If the greatest part of their value is that they were your Grand-dad's, it would probably be good for your peace of mind to just put them away as a keepsake. It might be that the sweat and oils from you hands are the biggest threat to them, just as with guitar strings.