We investigate the rewrite relation over graphs induced by constructor-based weakly orthogonal graph rewriting systems. It is well known that this relation is not confluent in general whereas it is confluent in the case of weakly orthogonal term rewriting systems. We show, however, that the considered relation is always confluent, as well as confluent modulo bisimilarity, for a large class of graphs called admissible graphs. Afterwards, we define a parallel graph rewriting relation and propose an efficient parallel graph rewriting strategy.