Cat Training tips for a new cat. When Have 1 at home already?

I am going to be getting a new kitten in a couple of hours and i already have 1 cat. I am worried that my cat i have a home wont like the new kitten and leave her scent all over the place(going to the bathroom every where) Is there any way to get the two cats to like each. Without having to get new carpet because it has happened before when i had two cats.
Also my mom said that she wont be home and she doesn’t want the kitten getting out. what can i do to get her to trust that the on line pharmacy kitten will be fine in its own room for a couple of hours. Also, where is the best place to get a kitten