You have 16 possible combinations, right?
Frame 1 - Frame 1,2,3,4
Frame 2 - Frame 1,2,3,4
Frame 3 - Frame 1,2,3,4
Frame 4 - Frame 1,2,3,4
Think of these as 4 sets of 4, where the first sprite's frame determines the set from 1-4, and the second sprite's frame determines the number within that set from 1-4
Since you have 16 possible combinations, what you can do is use Advanced Random to pick a random number from 0-15 (16 digits, starting at 0) without repeating. You can then translate this number into a two different digits. One is a set number from 0-3 (4 digits, starting at 0) and the other is a number within that set from 0-3
For example, let's say you ask Advanced Random for a random number between 0 and 15 and it gives you 5. We can translate this into two numbers.
First, let's get the set number. To do this we divide the random number by 4 and round down. This will give us a number that is either 0, 1, 2, or 3. This will tell you what frame the first sprite should be.
floor(5 / 4) == 1
So we are in set 1. The first sprite's frame is 1.
Then, let's find out which frame within that set we are. To do this you can use modulo to find the remainder after dividing by 4. This will also give a number from 0-3.
5 % 4 == 1
So this is the frame for the second sprite. Frame 1.
So 5 translates into Frame 1, Frame 1
0 would translate into Frame 0, Frame 0
floor(0 / 4) == 0
0 % 4 == 0
1 would translate into Frame 0, Frame 1
floor(1 / 4) == 0
1 % 4 == 1
4 would translate into Frame 1, Frame 0
floor(4 / 4) == 1
4 % 4 == 0
11 would translate into Frame 2, Frame 3
floor(11 / 4) == 2
11 % 4 == 3
15 would translate into Frame 3, Frame 3
floor(15 / 4) == 3
15 % 4 == 3
Each number from 0-15 will give a unique combination of numbers for Sprite 1 and Sprite 2
Let me know if you have any questions!