Every case is different- even with the same set of circumstances so it's important that we review each case individually in order to draft an appropriately tailored solution.
If you have cats that are not getting along, the first step is to separate the aggressor completely in a different room with everything he needs. Still visit and play with him.
If you have an adult cat that is biting or scratching and drawing blood, isolate them in a room with everything he needs by himself until we can talk to you.
If you're unable to enter the room due to aggression, use a blanket or cardboard to prevent poor behavior while providing care.