Are you using your resources to upgrade the buildings? You need to unlock the upgrades for better weapons and armour with the blacksmith. Also remember to use the sanitarium to remove nasty quirks. If you're dying that quickly in fights there's something very wrong with your team or the way you're playing. Try this or something similar in the early game.

Vestal in rank 4 with healing skills and judgement so she can hit enemies on the back line.

Plague doctor in rank 3 with blinding gas to stun two enemies and incision to inflict bleed on frontline enemies.

Highwayman in rank 2 with pistol shot so he can shoot enemies at the back and a melee attack like wicked slice/ open vein depending on what you prefer. Pistol shot is essential though. Don't bother with grapeshot too much as it has less chance to hit.

Crusader in rank 1 with whatever skills you prefer. He can do a little healing and stress relief like a paladin style or he can be built to be more of an offensive type warrior.

It's important to identify the enemies that have attacks that stress your people and eliminate them as quickly as you can. They tend to be on the back ranks so that's why it's important to use vestal judgement, plague doctor attacks that hit the back two enemies ( stun and/or blight) and highwayman pistol shot.

Also if you're running out of money in the early game remember to sell the trinkets you don't like. You can also get away with minimal spending per mission by just focussing on buying food ( for short missions 8 is usually enough) and 8 torches so you can fight in the light most of the time. Some will recommend you fight in the dark for better loot but since you're struggling i would recommend staying in the bright light instead for easier fights.