We have recently discovered three stray kittens down my brothers shed, we left them for a few days thinking the mom would return but did not. We contacted the RSPCA etc.. They could not help us so we passed the kittens to my sister to hand feed as they are only a week or two old. A couple of days later we have found 2 more kittens a lot healthier than the last 3 which says the mom was returning. Should we return the kittens back to the side of shed or leave things how they are?

After that long with humans, it's unlikely she'll accept them back, especially if she's feral. She may even kill them.

It's best to just keep nursing them, yourself.