Effects on the atomic structure and electronic properties of two-dimensional graphene (G) and h-BN sheets related to the coexistence of dopants and defects are investigated by using density functional theory based methods. Two types of extended line defects are considered for pristine G and h-BN sheets. In these sheets, the presence of individual doping increases the charge transport character. The coexistence of dopants and defects tunes the band gap towards lower values and causes the direct-indirect band gap change. The relative stability and the electronic properties of various BxNyCz systems are analyzed in detail. We find that the structural properties of these types of systems strongly depend on the orientation of grain boundaries and whether these are parallel or perpendicular to the extended line defects. The electronic structure analysis of the different systems evidences the shift of absorption to the visible region.