As mentioned, IS/VR can only cancel out the shake in your hands taking the shot, by sensing movement and offsetting it by moving elements in the lens. If your subject is moving, it's of no use and can actually impair the image quality as the circuitry is busy trying to counteract movements much larger than it was designed for. Having said that, all else being equal, it can allow you to shoot static images in low light that wouldn't otherwise be possible.

One thing to consider - if part of your shooting will be landscapes, 50mm is way too long. You may want to get the cheaper 75-300 and pair it with the 18-55. If you can swing the 18-55 and 55-250 that would be ideal, but I'd overweight being able to capture the images/memories over the marginally improved image quality.