Suppose that the tetrahedra are distinguishable, then the equally likely outcomes of tossing the two are:

(1,1),(1,2),(1,3),(1,4)

(2,1),(2,2),(2,3),(2,4)

(3,1),(3,2),(3,3),(3,4)

(4,1),(4,2),(4,3),(4,4)

Now your actual experiment has outcomes (a,b) where a is the smaller of the two throws and b the larger. So we can list these and calculate their probabilities using the above table of equally likely outcomes of the underlying experiment.

(1,1) 1/16

(1,2) 2/16

(1,3) 2/16

(1,4) 2/16

(2,2) 1/16

(2,3) 2/16

(2,4) 2/16

(3,3) 1/16

(3,4) 2/16

(4,4) 1/16

CB