The Dragon Quest series, IX in particular has an interesting concept with status boosting/decreasing. If you're not already doing it, in every boss fight, it is strongly recommended for your Priest to cast Buff starting with the squishy allies, and stronger allies if needed. Following that, they then should focus on healing, and keeping everyone's Buff benefits in place. Your Mage should always cast Sap three or so times, which is a spell which will be spammed even with the post game secret bosses. I don't remember the poison being too big of a tribulation, as long as you inflict hurt, and have your Priest healing, the fight should be over by the time the poison starts being too much of a problem.
As for the Minstrel and Martial Artist, they should just attack. I'm also assuming you have them trained in claws and swords, which are fabulous weapons for the two of them. In fact, 300 hours later, my Martial Artist still has claws, and is the biggest damage doer in my party!
I also had a Warrior in place of a Mage, so it may have been easier in terms of survivability for me thanks to high HP. However, I'd imagine having early access to Sap would do wonders for your party.
If not, then you can always grind Metal Slimes in the Quarantomb. Don't feel guilty about doing so, they're there mainly for that purpose! As well as do various quests and whatnot, as they make perfect excuses for extra grind time if the Metal Slimes running away gets to you, I know it gets me frustrated after awhile.
EDIT: Also the Contra Band grants resilience to poison if you really want to know.
Recipe: Gold ring x 1 + Poison needle x 1 + Special antidote x 1
Credits:
Dragons Den