I don't know much about the camera in question, but the reason you are getting grainy pics is because the pics are indoors. Sportsmode automatically sets the camera at a high shutter speed, and indoors there is not enough light for such a high shutter speed. You would need to widen the aperature to let more light in. I don't know if that's possible on this camera. Also the flash doesn't go off in sportsmode.
You would get really clear pics outdoors in good light with that mode.