All I can say is that myth of divine twins is fairly widespread throughout Indo-European societies. Somewhat less widespread, but still present, is the idea of a primordial murder/sacrifice responsible for creation/foundation.
I think it is more plausible to say that existing myths, half remembered by the Italians after they broke off from the Indo-Europeans, were molded to fit whatever historical reality transpired (rather than new myths being created wholesale in the historical period, as per Wiseman).
As to whatever historically happened, I guess we'll never know entirely. I do like Maty's idea of colonization from a mother city .... but then who is the mother city? Alba Longa?