To that end, they're not going to focus on killing the characters so much as intercepting them and getting them into the room with the golem and gorgons. Those two main goals are keep the characters fighting the big murder things and keep themselves alive. Soldiers, being the most flexible force on the field, are going to be goal oriented rather than target oriented. Since they prefer melee combat and are marginally more intelligent than the Gorgons or Golem, they'll seek out someone who prefers ranged combat and get all up in their grill. Gygans vastly prefer melee combat over ranged and will seek to grapple-stab-stab someone. They can't tell soldier from invader because they're too dumb. They try to charge whoever the closest not-prone character outside of their 20' gore range. Gorgons target prone characters with their charge attack, hit targets they can't prone with Petrifying Breath. It prioritizes any characters out of range last. Otherwise it prioritizes targeting the unslowed character first, then among slowed characters within melee it targets the one with the most dexterity. If being attacked by more than one unslowed character within melee and has slow available, it uses it. Stone Golem is going to be deterministic and unthinking. In the military, we would call this Command and Control. I would also include commands shouted to the soldiers to give them a sense of coordination.

I wouldn't hit with both Javelin and Breath at the same round. He's going to be less of a direct threat and more of an environmental one, looking for clear avenues to attack from. Gaius pelts them with Breath attacks and Javelins of Lightning.

Harpies are stuck in the cage so not really a factor, as far as I can tell. List: Gaius, Stone Golem, Gorgons, Gygans, Soldiers, Chondrus. Once you have the individual tactics, you try to work out any existing or potential synergies and either work to exploit them or keep an eye out for happy accidents. Some are easy, some are easier when you use, some are a bit harder to figure out. Start with the list of creatures you're using. I like to think of individual tactics first.

Gygan movie list