Before going to videos, you should do your research. Learn about each character, because all three of them are played very differently. Videos will only give you a visual of what players are doing, not how it is done. If you really want to become good with those characters, you need to master the basics of the game (inc. advanced technique basics) and you need to learn character specific advanced techniques & combos. On top of that, your prediction skills and gameplay patterns will play a huge part in your success or failure. It will also help greatly to have knowledge on all the other characters in the game, so you're familiar with your opponents movesets.
That said, I don't have a video camera so I don't record any of my matches. However, this is a nice video showing you what two fairly polished Marths look like:
Drago vs. Claw
I can't really help you out with Kirby or DK, but there are others on this forum that should be able to assist you. Good luck with your goals.
Linear Mode
