Did you played ToEE(Temple of elemental Evil)? Without blasting the Noble Salamanders in the node of fire at greater range while you are protected from spells up to tier 3, i see no way to defeat then. They can deal 20d6 damage while they are immune to fire.
As for making the combat deadly, a lv 5 ranger with 13 CON will have probably have 39 hp(11+7+7+7+7 6 is the d10 average + 1 for con), a critical hit from a heavy crossbow(d10 + 1~5, lets assume 4) can deal 28 damage.
