
Have they recently been wormed, or due for worming (either can account for looseness).
Also why are you measuring out eh food, the guides are hardly every anything like accurate and I have found the best method is to feed to appetite, so that a little is left after meals (Mum can then finish up).
As for rate of weight gain, if they are gaining and are well covered then the precise amount they are gaining will be individual.
At this age I would expect them to be poo machines, and eating each others faeces is not uncommon, you simply have to try and pick up as soon as anything is produced.
My own pups do very well on Arden Grange but are loose (yellow poos like a babies nappy) on Royal Canin, but at this stage any sudden changes in diet are best avoided as they will shortly be facing the stress of going to new homes. I would try giving AG for one meal and see how that goes, and if it seems to be improving things, next day two meals, then 3, then finally change over.
By replacing a meal at a time you can see if it will be of benefit, or not.