III-V semiconductors such as GaAs are widely studied as promising candidates for high-speed integrated circuit. Despite these applications for conventional bulk structures, their fundamental physical properties in the nanoscale limit are still in scarcity, which is of great importance for the development of nanoelectronics. In this work, we demonstrate that the III-V semiconductor MX (M = Al, Ga, In; X = P, As, Sb) in its two-dimensional (2D) limit could exhibit double layer honeycomb (DLHC) configuration and distorted tetrahedral coordination, according to our first-principles calculations with HSE06 hybrid functional. It is found that surface reconstruction endows 2D III-V DLHCs with pronouncedly different electronic and magnetic properties from their bulk counterparts due to strong interlayer coupling. Mexican-hat-shape bands emerge at the top valence bands of pristine AlP, GaP, InP, AlAs, and InAs DLHCs, inducing the density of states showing a sharp van Hove singularity near the Fermi level. As a result, these DLHCs exhibit itinerant magnetism upon moderate hole doping, while the rest GaAs, AlSb, GaSb, and InSb DLHCs become magnetic under tensile strain with hole doping. With an exchange splitting of the localized p_z states at the top valence bands, the hole-doped III-V DLHCs become half-metals with 100% spin-polarization. Remarkably, the InSb DLHC shows inverted band structure near the Fermi level, bringing about nontrivial topological band structures in stacked InSb DLHC due to the strong spin-orbital coupling. These III-V DLHCs expand the members of 2D material family and their exotic magnetic and topological properties may offer great potential for applications in the novel electronic and spintronic devices.