If the chicks came from a hatchery, the odds are they are not as closely related as you think. I'd go with what you have.
Inbreeding is how the different breeds were developed and is how breeders win championships at shows. You do need to introduce new blood every few generations to keep the genetic diversity up, but it is not a criminal offense. If there are bad recessive traits, inbreeding can bring those out. If there are good recessive traits, inbreeding can bring those out.
You might do search on "line breeding", using the search feature in the blue band at the top of the page for more discussion.