
My most recent litter was like yours hardly eating between four of them more than a tablespoon of mushy food, and that was at four weeks also. they were also the fastest weight gainers I had ever had!!! Interestingly enough by 5 1/2 weeks Mum had totally stopped feeding them.
I have started puppies that seemsed hungry or interested in Mums food on sloppy solids as soon as their eyes are open, and usually aimed to start them at about 18 days regardless, as I liked them on solids prior to worming at 3 weeks. These would take no more than a lick for over a week, and were only taking two meals a day at 4 weeks because they just were not interested, then suddenly they were eating rather than playing and at 4 1/2 weeks I had them on four meals, and as MUm shut up the milk bar it seemed with every meal they were eating twice what they had last time.
I always make upo more than they will eat and Mum (and several other vultures will finish off :D