Welcome to pet talk.
I am glad you stated your reason for wanting young kittens because now I can advise you that this is not always right. Young kittens will be pestery to an old cat. If you DO get 2 kittens, they will have each other, and that is good, because the senior cat will more than likely NOT want to play as vigorously as a kitten.
I work with a rescue group and if you would have come to us my advise to you would be an adult who has a calm personality. One that will not challance her as alpha but will simply accept her as boss and therefore more easily becoming the friend she needs.
JMO