
What you have described is perfectly normal puppy behaviour and you should not be overly worried about, puppies are often nicknamed Land Sharks with good reason.
When you have a problem like this it’s easy to think it’s never going to end and you will have the worst dog ever, I promise you it won’t be like that.
Your puppy is playing like she might do with her siblings and she needs to learn that humans are delicate and can’t take this kind of play, this is known as bite control. I see you have tried several things, but how long are you trying each of them? It does take time for a puppy to learn that biting is not acceptable and chopping and changing may well be confusing for the puppy and not teaching her. Saying no in a stern voice won’t work very well as apart from the fact she doesn’t know what No means she just thinks it’s part of the elaborate game she’s playing with you.
My golden retriever was like this. I tried stuffing a toy in her mouth every time she launched herself at my hand, but it didn’t work too well as she wanted to chew my fingers as they were part of me and that’s what she wanted, my attention. Withdrawing that attention was what worked for me.
I would get to my feet and go and stand in the corner of the room, arms crossed and totally ignoring her. She would jump up trying to get me to react, but I didn’t and she would finally give up and sit down looking sad and lost, that was when she got my attention back. But this took quite a bit of time to get her to realise that the moment she tried to bite me then my attention went and she was ignored. I had to do this every single time, but my finally she got it and the biting began to lesson round about 14 - 16 weeks.
I also found that giving her something really tasty to chew on helped, toys don’t cut the mustard, but a calf hoof (as smelly as they are) was far nicer to her, so her need to chew and bite went on that and she began to leave me alone.
So, equip yourself and the children with tough jeans and probably wellies so you all don’t get hurt when she jumps up, and when she bites all get up and stand in the corner totally ignoring her. Do this every time and it will work. Tell the children to become trees if she chases about after them jumping up and biting, it might be better to stop the children running about until the pup has learned not to bite and grab clothes
As to the breeder, yes it was very wrong of her not to tell you that the puppy you chose was not from the same litter and has different parents. I take it the puppy is not KC registered with a 5 generation pedigree demonstrating parentage?