As an emerging class of mechanical metamaterials with superior mechanical properties, shell-lattices possess smooth, periodic, and non-intersecting structures and are preferred for their open-cell topology from the perspective of manufacturability and mass and heat transfer-related applications. To obtain elastically-isotropic open-cell uniform thickness shell-lattices, a strain energy-based numerical homogenization and shape optimization procedure is proposed, based on a B-spline parameterized Monge patch model for representing the shell mid-surface within the fundamental domain. The whole analysis and optimization procedure is applied to the shell-lattices of P (Primitive) and IWP (I-graph-wrapped package) families, with the initial designs taken as the constant mean curvature (CMC) surfaces with different mean curvatures, showing that both families of lattices can...