Easiest way to be top cat is to treat the kitten like you're the mum cat. For a few weeks, when you pick her up lift her by her collar like mum cats do, if she's clawing at you, pin her down (gently!), take her away from things you don't want her around with a firm no. But she is a kitten and curious so will keep trying to get into things, it's what they do. She needs heaps of interaction and a certain level of roughish play, but not rough rough. It's kind of why I usually recommend if you get kittens to get two of them. They're used to being around their litter mates, so have their brothers and sisters to learn and play with. Kittens, like puppies, need a lot of time and attention. As for the poos, like everyone else said the food may not be agreeing but if they were on a different food with the home they came from, you need to slowly introduce a new one to them so their stomachs can handle it. And remember they are carnivores and so will need raw meat in their diets. Most dry foods have grains and they find it hard to digest it.