If mum has stopped feeding then I would be feeding 4-5 times a day too. I know when I picked up my first dobe he was being being fed 5 times a day and wasn't fat. They will usually eat till they are full at that age (in my experience anyway) so I would stick with the 4 times a day as you have been doing and then up the amount per feed as they get bigger. Does mum not feed at all now? not even the occasional feed, as that seems a little early to have stopped all together, but then you have a different breed.