Depends on the size of the moons. A couple of glorified asteroids like Phobos and Deimos won't give much but a bit of color and something to make the calendar interesting. A couple of Luna-sized monsters could have enormous effects on the tides, although the second moon would have to follow a much more distant orbit and tides scale to the inverse cube of distance, so even if it was more massive its tides would likely be weaker.

Google Gravity Simulator to get a tool to test the stability of your lunar orbits.