Err, the story of Vascaroon is only a legend for one, but since it deals with the creation of man, it's obviously a long long time ago, so why you think Laguna and Vascaroon are the same person is rather odd. There's also no reason to think they're close relatives.

Anyway, I first heard it on the White SeeD Ship, later in Tutorial, and finally saw it in Balamb on my second playthrough or something. An old guy there tells his granddaughter about Hyne's mysterious dissapearance (incidentally the basis for a lot of FE's theories...).