The water impact of one and twin free-falling wedges is numerically investigated by a Cartesian grid multiphase flow model. The effects of the drop velocity and the gap distance on the hydrodynamic behaviors are parametrically investigated. The numerical model involves a radial basis function ghost cell method (RBFGCM) for treating moving bodies and a gradient-augmented level set method (GALS) method for capturing violent free surfaces. A case of twin wedges entering water is simulated to validate the accuracy of the present method. Good convergences are achieved. Then, the water entry of one and twin wedges in free falling is considered. The interaction mechanisms between twin wedges are discussed by comprehensively examining the variation patterns of the slamming load, the moment, the local pressure, and the fluid field. It is found that the second slamming load and the huge pressure pulse occur at the transition stage at narrow gap distances. The hydrodynamic interaction has more significant effects on the local pressure than that on the global load. In addition, distinct hydrodynamic phenomena for twin wedges entering water are observed such as the connection of the pressure contours, the extremely large jet flow, formation of the cavity, and even the ventilation.