Is there a way in PhotoShop to reverse the image, so that the pictures can be then used as iron on transfers?

Something to try. This will fiip a single layer:
* Select All
* Edit > Transform > Flip Horizontal

Will this work?

That works, or depending on your printer you can set the printer to print in reverse.

On my Epson printers I have that option in the print setup as it is preparing for printing.

- Noel