"Cats do not share the litter box. One comandeers it and won't let the other use it or neither will use it."

From personal experience, absolutely not true - certain (cat) personalities may do that - we have at least one (allegedly human) poster here on Mudcat like that ... :-)

Kittens raised with their mother will share a try with little fuss, but they usually then prefer to go outside, unless it is raining and they can't find a dry place.

My previous 2 cats - raised together from kittens from different littlers from opposite sides of town cooperated, untill they were old enough to go outside.