Several issues abound here.
First the receptacles in the dining room cannot share any other outlets but the dining room and kitchen receptacles.
If there is only one breaker there is only one circuit. Splitting the circuit to run in different directions does not constitute two circuits.
To change from 12 gauge wire to 14 gauge wire would mandate that the overcurrent device be a 15 amp device.
If you are having this inspected then be sure that any and all receptacles in the dining area are on a small appliance circuit that has nothing else on the circuit.