Only fiery blood says that it adds a +3 feat bonus for fire attacks, but elemental echo and Shocking flame also add damage (provided by feats). I am unsure whther they stack or not. Do they?
Yes, they all stack.
Fiery Blood is a feat bonus, which means it does not stack with other feat bonuses. Elemental Echo and Shocking Flame's damage bonuses are not feat bonuses, they are untyped bonuses, meaning they stack with everything (including other untyped bonuses).