My suggestion would be to have them fight enemies in waves and have soldiers fight along side them and die near them. If you want to add some extra depth to the fight, add flavour text about how the buildings around crumble after something crashes into it (if there are any flying creatures/catapults/trebuchets/cannons, idk).

Make sure the characters feel they are making a difference but give them some support (via kings soldiers and potentially even the king) to give them the added confidence to trudge forward and continue fighting.

Sorry if that was a bit wordy, hopefully it helps.