ironchefmitty
Knife takes more practice especially when it comes to mountains. Don’t get upset it is quite a journey to take and it will bring you where you want to be. Just more patience and more practice.
If paint does not stick when you have paint on the canvas try to scrape it first to prepare base for a cabin. It may be a signal that paint on top of which you apply cabin has a big thick layer and quite a lot of oil in it. You may even consider using paper towel to wipe a base for a cabin to remove oil leftover after scratching.
With knife in general less and less pressure needed for each next layer as much pressure will be mixing layers of color.
Also for cabins I highly recommend take a pencil and draw 5-10 cabins on the piece of paper following YouTube videos about two point perspective. This is more important skill for new painters. After this you can go to step two and bring paint in the training. Take a canvas and build as many cabins you like. At the end you can scrape all the mix of colors and use it as mix for mountains, forest, etc. freeze those leftovers in a small plastic jar and re-use as needed. A little note brown colors dry fast compare to the rest of oil colors due to the pigment nature.
At the end if you get extremely mad at the cabins you always can paint cabin with a flat brush of smaller size and you will have more control on the angles to make it look like a cabin.
Painters of 18th century did not use knife for mountains or cabins, so everything is possible without a knife. Main important thing here - find the way that makes you happy when you paint: knife, or brush or fingers or any combinations of them.