Hi there.
This is an issue of scale mismatches in your assets. In older versions of these packs, I included three sizes for different RPG makers or engines. 16x16, 32x32, and 48x48 (a weird size that MV/MZ use). I did not make 64x64 assets by default for anything, though you can double the 32x32 or 4x the 16x16 to achieve this result.
However, I changed how I packaged more recent assets like the Free Cyberpunk character pack and some of the other packs. I no longer include all three sizes. Just the 16x16 because it can be manually resized by users very easily with graphics software like GIMP or Aseprite.
Can I ask, what RPGmaker or Engine are you using? Do you have a graphics program like GIMP or Aseprite?
If you do, you can probably fix this by taking the 16x16 characters you want to use and rescaling them 4x to work on a 64x64 tilemap. Personally, I develop in MZ and the default is 48x48 so my usual method is to upscale 3x to get a screen/resolution scale like this:
Different art style with different default scale, but you get the idea. With the same scale assets, but from a different theme, this is what Nine Realms looks like in RMMZ when scaled 3x to be 48x48:
This stuff can be complicated so please ask any questions. I should be able to help you fix this, but making 64x64 sprites is something you should be able to do easily without needing an update to the pack.