The following remarks are specalative:
There is a tremendous amount of diversity in the alien species found within the Saga universe and offspring from interspecies matings possess non-human characteristics from either one or both parents. Given that The Will and The Brand are the only non-trivial characters to lack any non-human characteristics, they are likely human (or very nearly human) siblings.
129.255.224.64 15:53, May 21, 2015 (UTC)Tom