well seeing as no1 else has posted yet i'll give some basic advice to the marth player. (I don't have good enough dk experience to advise that player).
Use more Fair, particularly against dk in the air, just stay away from his Bair. D tilt is hardly ever used, the same goes for grabs. Predict a roll and punish with one of these (your d-tilt moves you forwards slightly each time, has iasa frames on it, and is very powerful IMO). Anotehr thing you don't use enough if your forward b combo (or you stop short at 1-2 hits), you can use it in front or behind you out of a dash, making it a very versatile option of punishment for spotdodgers/rollers.
when you recover you sometimes set yourself up for dk's upsmash and u-tilts, try to be less predictable in your aerial recoveries. Same goes for for when dk is recovering. You are very obvious with your approach and intent to fair dk while he returns to the stage and he was able to see through it every time, try to confuse him by acting like you are going for him but then pull back (if he whiffs an attack, you get a free oportunity to hit him), or land on the edge and fsmash/d-tilt him. I noticed you roll alot, and i know roll is better now then before, but you make it predictable, only use it occasionally, and don't string them together so much.
i intended to make this brief, but it ended up being longer. Good match, i was hoping not to be bored watching it and wasn't. Gl and happy Haloing.