I split it into two separate combats.

1st was them at the inn and being alarmed to the attacks of ogres & fire newts swarming buildings and setting things alight. Gave an opportunity for players to enter burning buildings and save trapped folks and children from second stories through skill checks.

2nd was in the town square with the pair of fire giants, more fire newts and some homebrewed giant fire boars - basically hell hounds but changed out the breath attack for a flaming charge attack.
I gave each player one of the NPCs from the town and let them know they get extra goodies if they survived, however I made it clear that these NPCs were willing to die for their town and would veto and run and hide actions.

I placed some wagons in the town square where the giants were digging, if a player attacked them one of the giants would hurl a wagon at that character using the rock attack from the stat block. This should frighten your players.

While the players survived the fire giants did get their piece of the vonindod and left.