I know nothing about familly history research, but most (as far as I know, all) Adobe photographic software can use Intel's hyperthreading. So, as you move up, through i3 to i5 to i7, you will get improvements in photo processing speed, so it's a question of how far your budget will stretch. A decent amount of RAM (6GB+) helps, as does a good amount of fast access storage.
Graphics tends to be more of an issue with video, but, if you believe all of Intel's sales hype, the HD4000 graphics on the latest Ivybridge series is very good.
If you check out Chillblast's website, they have a whole section, on photo and video systems. Their high end offerings are very much video orientated, but more modest ones would be suitable.