Which iteration of Tieflings? Anyway, after the various changes both within Planescape and over editions, I'd consider a Tiefling to be Base Race, Some other race blood (lesser), infernal (lesser). Aasimar didn't change much as far as I know, which is pretty much only PS and 3.x Edition. Given the original tiefling description, I'd do something like Human/Elf Blood, Lesser/Infernal Blood, Lesser. Aasimar same thing: Base, something lesser, celestial lesser.
Blood Talents are made of existing talents from the master talent list or even the monster talent list.