I have done something similar, a wiki with lots of images but in my case mostly one per tiddler. However, the idea is the same with multiple images per tiddler.
I store my images in an external folder and all files have a name like CS121.jpg, where the 121 is just an increasing serial number stored in $:TLS tiddler and incremented after each successful add.
Then I have a button on a special tiddler that reads the next serial number and creates two tiddlers, one titled CSserialnumber that contains the canonical link to the image file and a second given a unique title that contains the transclusion to the first.
It would be a simple procedure to call the create code between two serial numbers.
Have a look at Central Street Archive and have a browse at the
$:/TLS/Actions/Add New Item tiddler. Here I add two images to the same tiddler.