This is actually quite easy once you know how...
Open the background image with GA 5. Then click the "Add Image" button on the Standard toolbar.

Find and select your little fight scene gif file and click Open.
As of this moment, you should have the Object Manager full of the objects from your imported animation, and all of them should be selected. Select the Pick tool, and make sure the Attribute toolbar shows "Move active object(s) only" checked.

Click and drag the objects to where you want them.
Next, you'll need to use the "Synchronize Objects" button

on the Standard toolbar. Click that, then select these options:
Select source image - leave this at the frame showing.
Objects to synchronize - select Active only
Attributes - select X offset and Y offset only.
Apply to All frames.
Click OK
That should do it.
Note that the frame delay from your small animation will not be preserved.
The other way to do this is to open the small animation first, then add the background image. On the Object manager, you'll have to click and drag it to the bottom of the list. With that object still selected, click Edit, Crop Canvas. This will let you see the whole background.
Next, you would position the background to where you want it. Repeat the Crop Canvas to again get everything properly placed.
You would use the Synch button as in the previous example, having only the background object selected in the Object manager. This time, you would also select "Visibility" in addition to X and Y axis.
Hope this made sense!