A. There is always going to be some amount of conflict in a multiple cat home. Felines are territorial animals and the dominant cat continually reasserts her dominance by "beating up" on the submissive cat. Usually the dominant cat will approach the other with hissing or stalking behavior. If that doesn't chase the submissive cat away, she will progress to swatting, wrestling or biting. These kinds of interactions are normal. However, if the submissive cat is being hurt or is hiding excessively, then you need to intervene.
Often a surge in dominance behavior is associated with a perceived threat to her territory. Changes in the household such as a move, a new pet, a new baby, or new cat in the neighborhood can all cause increased aggressive behavior. But the most common cause is fighting over resources. Your cats' resources are their space, food and litter boxes, and to some extent, their people. Because you live in an apartment, they are probably fighting over resources.
But, you say, they got along great while they were young. It is typical for cats to start to fight when one or both reaches social maturity, between 2 and 5 years of age. This is when they start to recognize what their resources are and whether they need to have control over them.
I would recommend providing two sets of food and water dishes and two litter boxes in separate locations. Ideally, the cats cannot see each other from each location. Watch the cats closely to see if they are fighting over a particular space such as a preferred chair or cat tree. You may need to provide additional "prime spots."
Three-dimensional spaces such as kitty condos or cardboard boxes will increase their perception of safety. If they only fight in front of you, perhaps they need more one-on-one attention with you. Your goal is to reduce the aggression to an acceptable level. It will probably not be eliminated completely.
I do not think declawing would help this problem in any way. You can learn more about declawing at www.eastbayspca.org/petownership. Additionally, you may want to have the bumps on your cat's head checked out by your veterinarian to make sure it is in fact trauma and not dermatitis or a flea allergy. Your kitties are fortunate to have an owner who cares about them enough to help them solve their kitty problems.
--Dr. Heidi Strand is a veterinarian for the East Bay SPCA in Dublin. She has lived in the Tri-Valley for 10 years with her family and an assortment of four-legged friends. Questions can be mailed to 315 Diablo Road, Suite 100, Danville 94526; or e-mailed to email@example.com. Her column runs every other week.