As the other person noted, pill pockets or pill wraps help a lot. My more difficult cat initially kept spitting them out even with the wrap, but he eventually learned that I'm going to try again and again, and he doesn't get the treats until he swallows, so now he's pretty good at swallowing on the first try AND I can get away with the occasional unwrapped pill.
The other trick I used was using my younger cat to help train the older one. I started off using a syringe of water, followed by treats to get them used to the general process and the understanding that they get treats after. My younger cat would line up for another syringe of water knowing he would get treats, so we'd do a few rounds of syringe water every evening, and I just kept doing that until the older cat got curious enough to voluntarily participate. Once they were both voluntarily participating in the syringed water, they would at least come to me for pills, so the only fighting was to get them to swallow.
Some tricks to encourage swallowing include holding their mouth shut and stroking the underside of their neck, and/or following that pill immediately with a syringe of water.
