I think you have done a reasonable job with the equipment at hand - the critique may seem over the top, particularly as I myself try not to use flash other than as infill. There will be many more expert on this site
Two main problems:
1 The throw of your flash didn't illuminate the badgers' bodies
2 Undiffused on-camera flash tends to produce undetailed highlights
Supposing the flash output is fixed, to increase its effectiveness you might use a bigger aperture than F8; you might consider a reflector(s) of some sort (hoping the badgers are accommodating) - even a piece of cardboard cover ed in cooking foil can do a job outdoors; you should consider getting the light source closer to the subject. Diffusion could be achieved as simple as a piece of translucent white plastic (eg a milk bottle) over the flash head, or even a piece of greaseproof paper. Unfortunately diffusion is likely to reduce flash performance.
An alternative aid would be to locate a diffused flash off-camera - perhaps remotely activated. If on-camera, get as close as you can and set your camera appropriately
You've done all the hard work to get them there and gain trust; so if you continue with the feeding, they'll probably come back. So you'll be able to experiment.
I'm lucky that my animal photography is largely confined to horses, dogs and cats which operate in daylight. Even then white hair and black hair provide challenges. It took me a long time to work out that it was (natural) light that was causing my problems
Some useful sites:
Keep working at it