This game will be very hard to make without the pathfinding, but the standard behavior doesn't work with tilemaps.
There are a few plugins for grid-based pathfinding, you definitely should check them out:
Also, Bullet behavior is inaccurate and hard to control. Instead of Bullet, use MoveTo, it's a great behavior, very easy to use:
Why do you have like 6 or 7 tilemaps on top of each other? Usually you need 1 tilemap with Solid behavior where you define tiles like walls and trees. And another tilemap with grass and all other scenery objects that you can walk on.