Let me add one of my favorite bits about running two fans in parallel off one mobo connector. Yes, do it! (And the consensus around here seems to be that most common mobos can handle the start-up current for 2 fans per output connector, but maybe not more.) When you connect two fans' motor wires together so they plug into one mobo connector, I recommend you do NOT connect together the two fan motor speed signal wires. On a 3-pin fan, these are the YELLOW wires. By all means connect together the two black (Ground) wires that go to Pin 1 and then two red (+VDC) wires that go to Pin 2. But the Yellow wires take pulse signals (two per motor revolution) from each motor back to the mobo. It you connect both wires together, the mobo gets a mess of two overlapping pulse trains and cannot make sense of them. Connect only ONE yellow wire to Pin 3 of the fan connector; leave the one from the second motor unconnected.
For 4-pin fans the color codes are different. BUT the first three pins are the same, so again it is the wires to Pin 3 that are for speed signals. Pin 4 has the PWM control signal and these two wires from the two motors should be connected together.