Can you elaborate about the word "aligned", "chopping", and what you need?
From your description, looks like it is a very engine-specific issue. Everything in my tilesets are already perfectly aligned in 16x16 px. The animals being sprites - not tileset, will always subject to so called "proportion". That means they may exceeds 16x16 px when considering body form and species.
This is the example of how my tilesets should be set up for 16x16px tilesize, the engine used is Godot for this one:
And as already written in the Contact Me, due to vast abundance of game engines available on planet Earth, I can't provide technical supports for each game engine. Please refer to the correspending tileset set up tutorial for each game engine you use.