Should the Elemental Affinity for these characters extend to other bloodlines connected with their element.
For example should a Sylph Sorceress be able to use her Air Affinity with the Djinni or Stormborn Bloodlines.
Thoughts?
Give us a more cogent example of what your asking, please.
According to rules, a Sylph Sorcerer gains a bonus if belonging to the elemental (air) bloodline. (+2 effective charisma for all sorcerous effects regarding to the bloodline)
Since Stormborn appears to be a variant of the Air bloodline, it might be logical to give a Stormborn Sylph Sorcerer the same bonus, as well.
Same would go for the Djinni Bloodline. According to description, a Sylph has some Djinn, Air Elemental or the like in her ancestry... which results in the aforementioned sorcerous affinity. When the only thematically appropriate bloodline was Elemental, we were all set. However, since a Djinni bloodline appeared in the rules, it is quite questionable why a sylph descended from a Djinn should be affine to Elemental (Air), but not to Djinn.
Of course, the same effect runs through the other four elements as well.
So, my opinion is the affinity for the Genie-kin should apply to their elemental bloodline, their Genie bloodline, and the variants thereof... choose one. No, you won't get a double-up if you pick crossblooded: Djinn / Stormborn.
However, unless something official is stated (*cough* Races Guide *cough*), this would strictly remain a house rule.