My cats always play together, and sleep together...they clean each other and the younger of the two actually tries to "nurse" on the other (which btw is a male)...they are about a year apart...same Mother, different litters.
i had 7 cats now 5 because 2 disappeared.the older cats are always grumpy when they see a younger one and try to keep out of the way while the ones which are the same age hang around with eachother.must be those wild cats