How do I automate auto-blend for different numbers of files/layers in Photoshop?

I am in the process of updating hundreds of files of old content. I am looking for a way to automate this function as it will need to be repeated hundreds of times. I need to merge 2 nearly identical gifs of indexed colour to create a single gif of indexed colour as follows:

Auto-blend seems to be the easiest way to do this, however, I can't see how to avoid doing this process manually. The variables in this process are:

• there are 2 or more different files that need to be merged (normally 2, but up to 5)
• the files in a group have the same name with a sequential letter appended to the name, eg. 1234a 1234b
• while each file group is the same dimension, different groups have different dimensions

The original .gif files were exported from Flash. However, the template is rather complex, and no tool was created to export the images. Manually exporting new gifs from Flash or creating a Flash panel to do this is more time consuming than using auto-blend manually in Photoshop.

Is there a way to create a droplet, or automate this process?