To say the members of Run Boy Run have chemistry is an understatement. Siblings Matt and Grace Rolland perform alongside Matt’s wife, Bekah Sandoval Rolland, and her sister, Jen Sandoval. Completing the group, upright bassist Jesse Allen is anything but the odd man out. Rooted in the musical traditions of Appalachia, the band’s 2013 debut So Sang the Whippoorwill turned heads — including Garrison Keillor’s, who twice-invited the Arizona-based musicians to perform on “A Prairie Home Companion.” The rising stars meld bluegrass, folk and old-time tunes with three-part harmonies on their national tour in support of sophomore effort Something to Someone.