puppies are just over 5wks now, and getting 4 little meals a day, and doing really well, my question is, when and what is the best way to get them to stop feeding from mum.

Leave it up to Mum. 

My girls often still allow pups to have the odd suckle right until they go.  Pups that stay have never been allowed to feed much beyond that and my girls have been totally dry by 12 weeks the time they are spayed after their last litter.

My most maternal bitch kept feeding her pups to about 9 weeks, was spayed at 12 weeks and now has a firm undercarriage with the pups just over 4 months old.  She had huge heavy boobs, and I am very surprised she has gone back so well.  This was her third litter.

I have never restricted my girls from feeding for as long as they liked and all have been in fit enough body condition to show by the time pups are 4 months old (even if their coats are not back enough).

I too would leave it up to Mum, that way she will dry up slowly without becoming engorged, once they get teeth can speed up the natural weaning process too.