It's relatively simple to do a axis-aligned box collision
First, you need to define the X, Y, Z radius of each object (size)
Then define the position of each object
Then get the absolute distance from each object to each other object in X,Y,Z (xd = JO_ABS(x1 - x2) etc).
Then you know if any object's distance to the other object minus the radius of both objects is less than 0, they are colliding.