Since you posted this in two different places, I'll just answer it here...
There are no signs of Lacus and Ferid being related, but it could make for an interesting fan fic. As far as we know, Ferid has not sired any vampires himself. When he turned Crowley into a vampire, he used Saito's blood instead. When he wanted Mika to become a vampire, he made the situation force Krul's hand instead of doing it himself. The Vampire Shahal OVA had Ferid turn Shahal into a vampire, but that vampire was far too weak to have been sired by a seventh progenitor and the OVA isn't canon anyway.
Lacus is a guard because, like Mika and Rene, he's stronger than the average vampire but does not have a progenitor's status.
Ferid has not given Lacus or Rene any special attention.
Although there are a few similarities between Lacus and Ferid's personalities, there aren't any signs of them being related or having any connection other than business. It is a fun theory, though