Kitten littermates seem to grieve when their sibling dies. They may stay close for a while after the death, and sleep more than usual. If they are separated, they will probably spend time together again within a few hours of being reunited.
Do kitten littermates get along?
Kittens can be very affectionate with each other before going out into the world on their own. When kittens go outdoors in an intact social group, there is usually much play-fighting between siblings that leads to little scratches and bites (this behavior may increase during adolescence). The older kittens do not always take charge but can appear domineering if things don’t go their way!