Yes, you can change the DPI to 300. No, this won't make the images any sharper. They started out 1280x1080, 72dpi. Merely increasing the DPI won't make them higher resolution. It will still look like video. If you hire a photoshop pro, a graphics designer, they might have a few plugins in their toolkit that can help, like Genuine Fracals that help with upscaling smaller images, plus know-how on how to deal with this. But it won't look like it originated from a 12 MP camera.
Suitable for printing? That's up to you. How does it look to you?