i have an electrical box, single gang for 1 outlet. It has 3 seperate wires coming into the box, one coming from another outlet, that will supply the power, and two wires leaving the box to go to two seperate outlets. all three wires have a ground.
Two ways to do it.
Find receptacles that can accept four wires under the screws. These are called back wired and have a flat plate under the screw. One wire can go under each side of the plate(two per screw) allowing four wires to be connected to each side.
Pigtail the three wires with a short pigtail of the same gauge and colour. The pigtail connects to the receptacle.