I always used the silver heron sword as a pally vs ahtiehil, no noticeable difference in damage output, so I don't think they have a silver vuln.
Not sure about fire or light, but guessing probably not. (mummies make more sense for fire with the whole bandages thing)
And black light is negative energy, so a Lich should be immune to it. Or did they tweak things like they did with storms and water so that they have like a 90% resist instead of full immunity.
But liches can get phylacteries that make them immune to holy as well, think it comes from pally corpses.