They're based on a 16x16 tilegrid base size. That means that some monster sprites may be larger than a single tile but scale with characters and environments based on that size.
Most of the monsters are not four directional. They're designed for use in full movement-based action-combat systems (like Zelda instead of a turn-based RPG).
Some of the monsters, like the marauders in that gif, have two diagonal directions (up and down) which can be flipped to make four directions for most real-time action combat systems.
If your game is something that specifically requires four cardinal directions for every enemy design (like a tactics system where it matters which grid direction to target), then these monsters might not be the best solution for that project. The human characters in my Elements sets have animations in 4 directions, that might work better for your needs.
Thanks!