We have had eight litters where all puppies have thrived.
At 4 weeks your puppies should be in the process of being weaned and eating whatever you want them to have once they are independant – ie moistened all-in-one food or meat and moistened biscuits around 5 times a day. They should spend a substantial time away from their mum as she will be getting fed uip of their sharp little teeth and nails.
At this stage ours are usually also having goats milk to drink Mum will still be spending the night with them, but she will only be supplementing the food you are giving.
Good Luck
Maud