They are still a bit young to be weaned from mom. It's OK to go ahead and introduce them to softened food at this point and they may take a small nibble here and there, but it will not be enough to sustain them at this point. (Most likely, they will just want to roll and play in it at first and make a big ole' mess!
)
5 pups at that age can take their toll on mom though, so be sure to keep an extra eye on her.
Make sure you are supplementing her calcium intake to help her produce the milk the pups need and to avoid some serious complications with eclampsia.