chomping on the litter is very normal at this stage, just be carefull if you use clumping (it can cause impaction)
its quite normal for momma to come into heat and even get pregnant while nursing the current litter unfortunatly so watch her closely, shell likely try and slip out for a rendezvous
n terms of introducing real food, i usually start offering canned food as soon as the teeth start comming in (around 3 1/2-4 weeks) i allow momma to nurse untill she says shes done (called abundance weaning) and they typically go untill 6-8 weeks of age still taking occasional meals fro momma, but i find offering wet food early and following an abundance method the kittens get to wean at their own pace...
ive got a litter of almsot 7 week old kittens, and 1 male started eating wet food at 3 1/2 weeks and hasnt looked back, the oldest male didnt try the wet untill closer to the 4 week point and now seems to prefer it over nursing...but the female isnt too interested in food yet and stll prefers momma...
as long as momma is n good shape, theres no reason to force wean.
i never do soaked dry food for kittens, i simply feed a high quality wet food (first incredient chicken or lamb), ill add a little warm water for the first week or so to make it more of a thick soup but by 4 weeks they easily handle the wet food straight from the can...
at about 5 weeks ill start leaving a bowl od dry kitten food down 24/7 for them to pick at, but cats do best on a wet food diet as they dont naturally drink much...
doing the abundance method though sometimes you have to be a little more varied on the date you allow them to go home...
the female is staying anyway so in not worried about her being slower to wean, but at this stage id be happy to let the yonger of the 2 males thats eating fine go at 8 weeks, but will probably keep the older of the 2 males thats still accepting some feedings from momma untill closer to 9 weeks just to be certain hes ready to go and thrive.