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 be made to achieve elastic isotropy by varying the shape of the shell mid-surface. The stiffness properties of the elastically-isotropic shell-lattices can be further improved by introducing Young’s/bulk modulus maximization into the shape optimization algorithm.