I'm not sure I understand. You have 12 separate animations that you want to put together in one animated gif in a grid layout like below?
If all the animations are the same size and number of frames, that's easy. If they're not and you want them all to loop the same, you run into the problem of frame count.
Let's say one animation is 29 frames and another is 39. The first has to loop 39 times, and the second 29 times for an even loop. It's still doable, just may result in a giant file because you need to find the least common multiple of the frame count for all 12 images.
May I ask what this is for? I see little reason to have them all in one file anyway, since you could just put the separate images on a website arranged in a grid and not worry about the above at all. Another issue is that a gif only gets 256 colors per frame, so putting ones that use a lot of colors together can kill the quality.
In short, I can probably do what you're asking, but I'm not sure I understand why you would want to. Or I may be misunderstanding what your end goal is, in which case please be more specific.