Using image editing software like Photoshop, select File > Import > Video Frames to Layers and choose all of the GIFs you want to combine. Select all of the animation frames in the first GIF, then copy them by selecting Window > Animation. Next, move to the next GIF, choose where you'd like to insert the previous GIF, then paste in the copied frames. Repeat with other GIFs you want to add, then export the finished amalgamation when you're done.