The questions you are asking are impossible to give a totally accurate answer to so here is my experience with kribs (please note - I only had one pair of kribs and this example is of three spawnings of the same pair ) -
The first time both parents raised them. It was at about 2 weeks that they started to be allowed to move away from the adults, without the adults bringing them back. The parents both raised them and remained with their fry until they were big enough to sell on.
The second time I spawned them, once they became free swimming the female nearly beat the male to death and I had to remove him for his own safety. Once the fry were about 1cm I placed them into their own tank and returned the male. They spawned immediately.
Third time, the female bullied the male so I removed them. She then proceeded to eat all the fry herself. A couple of days later I returned him and about 2 days after that they spawned again.
I think there is no hard and fast rule.
Suggestions -
Observe the adults carefully and also the number of fry with them. If one of the adults is being bullied or is away from the fry (hiding) remove it. One adult can raise them alone as long as they are not in a community tank.
If the number of fry is decreasing consider siphoning them out and placing in their own tank to raise.
Brine shrimp (hatched), microworms is good starter food.
Decap brine shrimp, novotom and daphnia as they start to grow.
Finely crushed pellets or flake eventually leading to normal sized flake/pellets.
Bloodworms.
As with all fry, be careful not to overfeed and pollute your tank.