Frame challenge, what you really need to do is medicate two cats successfully, not necessarily at once. Or in other words, medicate one cat without showing the other cat that it is an unpleasant thing.
I'd advise against trying to press the issue when your cats are already resisting or fleeing. While you might be successful this time, you'll make the next time you need to give them their medication even harder.
With daily antibiotics, it typically is not needed to give it to them at exactly the same time, usually it is perfectly fine to give them in roughly the same 6 hour window each day.
So if you started an attempt and it isn't going well, consider aborting before the whole process gets too stressful for you or the cat.
That said, giving medication to particularly difficult cats is never a fun exercise, but it can be a lot easier for all involved parties if you follow a good routine.
You first need to relax.
If you are not relaxed, first try to calm yourself down before you try anything. Your cat can smell your anxiety from two rooms away, it will notice the variance in your breathing pattern, and it'll know something is up right away.
If you are not relaxed, your whole body is basically a giant roaring siren warning your cats of possible danger.
I know this is easier said than done, but it really is key. Do not think about what could possibly go wrong, instead remind and reassure yourself that you will succeed in the end, even if it takes a little while longer.
You then need to get your cat to relax.
Ideally, wait for a moment when your cat is already resting. Bring the medication with you, but do not offer it to the cat yet.
Sit down next to your cat, and pet it, scratch its chin, whatever typically works to get it to purr.
The idea here is to give a clear signal that nothing bad is going to happen.
Give this a good five minutes (depends a bit on the cat, but you know your pets best), reinforce the point that nothing bad is going to happen, and that you are coming with good intentions.
Gently offer the medication.
The key here is offering, as opposed to administering. While this is specific to oral medication, you ideally want your cat to take the medication voluntarily.
It will most likely not work right away, and here you should observe the reaction of your cat.
If it gets agitated, put the medication away again, and go back to step two.
If it only refuses to eat it but isn't getting agitated, you might consider placing the spiked treat in front of it. Continue your petting, and give it a minute or two, it might decide to eat it at some point.
If you are still unsuccessful, abort the exercise and don't despair.
You might not succeed right away, despite doing everything right. Always try to end the exercise on a good note, if you notice your cat getting too agitated or you are starting to get anxious, better stop and try again later.
If you are successful, praise and reward.
Once the deed is done, give some positive reinforcement. Continue the petting for a while afterwards, give the cats their favorite treats, have a play session.