Cats are lactose intolerant so milk is not needed once weened. Mum's milk gives Phoenix all the nutrients & antibodies etc that she needs. So as for milk, kitten milk (kitten replacement milk) or any lactose free milk is not needed unless she comes home with you before 8 weeks old. I had a kitten we had to bottle feed as she came home with me at 5 weeks old because her mum wouldn't have any more to do with her or her brother.

First vaccinations are at 8 weeks old and usually 4 weeks later she will get her second round of vaccinations. She will be good then for 1 year. Spaying should be done at around 6 months. It is much better to spay before the first heat cycle. Spaying before the first heat cycle (usual at 6 months or so) will decrease (not eliminate) the chances of Phoenix getting certain types of cancer (mainly reproductive cancers like mammary cancer, ovarian cancer, uterine cancer etc). There is a significant decrease in the chances, that being a decrease of about 50%.

Check out this
site for some info. There are many many more out there that will give you supporting information as well as additional information.

As for the hissing at your sister...Phoenix may need some more interaction with people. She could very well just be scared. Also as for Phoenix's mum chasing things that no one sees that isn't all that strange. She could just be bored. She is obviously used to coming and going and occupying herself in the great outdoors. That's a pretty big playground for a kitty so being confined & having to care for a baby is most likely a very boring venture for mum.

I am sure there is lots more to tell you but my mind is a muddle now so if I think of anything else I will post.

Oh, one thing. Do get her spayed whether you intend to let her out or not. It is better in so many ways some of which are in the link I provided. Try to spend some time with Phoenix as much as you can before she is ready to come home with you & maybe leave an old tshirt or something for her to get used to your scent.