Two kittens. Always two. They are a nightmare when they are single. Read this:
http://meowcatrescue.org/...gle-kitten-syndrome/ The shelter I volunteer at, linked above, requires kittens in pairs unless you have an adult cat 5 years or younger already in the house. See link as to why.
It doesn't matter if they are related, it is whether they are bonded. Whomever has been taking care of them should know which two would want to go together. We have foster families who raise kittens until they are old enough to be adopted. They always give us info on who needs to go together. They aren't always related but they luuuuve each other anyway.
Also, please consider an adult cat. We have bonded pair adults who look for a home together. They could be together for 5 or 6 years, lose their home for some reason, and it would be too traumatic to separate them so we require they go as a pair.
Or a single adult cat. This time of year it is harder for adults to find homes because everyone wants kittens.
Astro says "We grown ups like to play and give love too!"
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Jen "In order to keep a true perspective on one's importance, everyone should have a dog that worships him and a cat that will ignore him." - Dereke Bruce