the two that keep fighting... are they young males that haven't been neutered?

if so... it might be possible they are having a territorial conflict with one another?!

the little one looks slightly malnourished... possibly parasites... or is the young one getting bullied by the others maybe?

hard to tell what's up without more details.

it would probably be best if you try to contact some other vets in your area...

ps: !CATtip 100 CAT