I have a 12 wk old German Shepherd puppy shes so mouthy and she nips and pulls our pants when we walk.?

We have tried redirecting her by giving her toys, if this doesnt work we grab her by her scruff, like her mother would do and give her a firm "NO" She also nips and jumps on my 5 yr old and 3 yr old grandchildren.I want to make sure we arent doing anything to make her aggressive. She is a very submissive puppy as of now and can obey all simple commands (sit, down, stay,.) but this biting is nerve racking. Any advice on correct disipline and or training would be greatly appreciated.