As for the Kolsch, the grain itself is nothing out of the ordinary for a Kolsch, but the hops are definitely. Kolsch should have low floral. spicy or herbal aroma, ditto in flavor...but the Columbus has strong citrus notes and Lemondrop adds more citrus and herbal notes. I would say enter it as a Blonde Ale...you really need to drink some while looking at the style guidelines to decide.
As for the Chocolate Marshmallow Porter, that's a tough one without tasting it. Is the chocolate just from chocolate malt or are you adding chocolate too it? Can you taste the marshmallow or did it just add sweetness? I mean nothing is stopping you from entering in American Porter, but you need to have a good hop presence in that style too. How strong does the chocolate come through? If you added like baker's chocolate, you may want to consider 30A Spice, Herb or Vegetable beer...chocolate is considered a spice, so if you can really pick it up, that might be your spot. Third option...13C English Porter - has a more restrained roastiness and is sweeter than American Porter and "chocolate" is used a lot in the style guidelines, though the reference is to chocolate malts. But if the marshmallows and chocolate created a sweet beer, this could be the spot. Last option, but not likely worth is would be 31B Alternative Sugar Beer - which says:
An Alternative Sugar Beer is a standard beer (Classic
Style or not) with added sweeteners, including fermentable
sugars (e.g., honey, brown sugar, invert sugar, molasses,
treacle, maple syrup, sorghum), unfermentable sugars (e.g.,
lactose), sugar alcohols (e.g., sorbitol), and any other
sweetener (natural or artificial) that affects the flavor profile
So marshmallows and chocolate (if you added) are fermentable sugars you added, so could play there. So I guess I was not really any help on this once since I gave you the 4 categories that it could fit into. Like I said, you really need to taste your own beer vs the style guidelines and decide where it belongs. One competition saying is "Enter your beer based on what it tastes like, not on what you attempted to make"
Also, there is nothing stopping you from entering it in more than one category. I did that once with a Pre-Prohibition Porter, entered it as Pre-Prohibition, English Porter and American Porter...it took gold in the first two categories.