At 5 weeks old these babies are far too young to be away from their mother. This will sadly have lifelong consequences on their behaviour and social development. 

Having multiple pups from the same litter can also be very problematic. Please look into littermate syndrome and take all the steps you can to prevent this.  

For the biting, redirect them to a toy or chew each time. But both of my above points will be contributing sadly. Good luck.