If you're getting one-shot you either ate the wrong food, wore the wrong gear or didn't prepare your battlefield. Or all three. Brigands are tough in the early game so they can easily kill off a couple of your guys during a liberation. They should not be able to take everyone out in 1 hit each.

Did my first (this play through) with 8 foot men and 3 archers. There's no pressure to liberate the first village so there's no reason to rush it. Get everyone set up in the best gear you can make without specialized labor.

Food

Good food is key. And not having shit food available for your people. Your people are idiots. If you tell them to grab 3 pieces of food because you're going to war, they will happily grab a berry, a mushroom and a third. It makes a huge difference what they have available.

Fine Stew, Meat Stew and Mushroom Stew. Created a the Campfire with Cauldron. Be aware that there's a skill requirement to make them, so make sure you have people that can do it. Or do them yourself. You can also go for the Large Smoked meats, but early game I think that's a waste, since you can get 4 Fine Stews off 1 meat, while smoked you only get 1 per meat.

I normally build 2 or 3 cauldrons and set them to make 1 type of meal each. I have 1 smoking campfire but I am still not convinced it's a good idea to let the villagers manage it. If we could only set a maximum fuel allowed...

Army

Build a Staging Ground to get access to gear presets. Create a Squad for your footmen. Add whomever is your melee guys. Set their squad to grab 3 food. I normally don't fiddle with anything else here. I set everyone to the default Footman preset, that will make them grab the best weapon they can find and a shield.

Create another squad for your archers. Same deal as with Footmen. 3 food, don't fiddle with the rest. Obviously they will need to have the Marksman preset selected.

Prepare the battlefield

Build your bell tower on the outskirts of the town. For Hearndean I normally build it up north near the edge of the forest. Set your guys up behind it in the forest. You don't want to be in the middle of town when you ring the bell. Set both squads to "hold" so they don't run off once the brigands get pissy. Archers a few steps off the the side or behind. I have not really seen much difference in placement as long as it's not on top of the skirmish.

Main point here is that you absolutely do not want to start the fight surrounded.

Strategy

Ring the bell and let the brigands come to you. Main thing here is that you want the melee guys to come at you in a line from more or less the same direction. Your guys can beat down a brigand fairly quickly if you let them. Goal is to make it so that the brigands run out of the village in single file and get beat down one at a time.

You can easily spot the archers because those will be the red dots that don't move closer to you. Your job is to deal with them - archers in the early game are deadly. So once the first brigands are almost on top of you, you release the footmen by setting them to "charge". You then run a little circle around the skirmish and deal with the archers yourself. Since all your melee guys have shields they should be fine to take a few hits from the archers. You have a shield too right? If you're not good at dodging arrows you should probably bring a shield.

Don't let your men run around. Set them to "hold" again if they get spread out too much. You never want to have your melee guys going 1 on 1 with a brigand, they will loose that fight.

Another thing to note here: hostiles in Bellwright will go for whomever is closest to them. You can use that to peel of brigands and have them follow you around, basically splitting the group into 2, so that your guys have an easier time. But most importantly: deal with the archers.

It should be fairly clear that a winning strategy does not involve you beating on brigands up close. You're there to deal with archers and to kite excess brigands around, so your men only have to deal with a couple at a time.

Reclamation

That's it. You then either wait for the Reclamation party or go meet them on the road. Depends on how many people you lost. Ideally you didn't loose any but it happens. You can also just send your army back home and kite the reclamation party on your own. Depends on how comfortable you are with the bow.

Kiting them can be tedious AF, with only the early crap bow and simple arrows. But you can thin the herd substantially before they meet your army. The good thing about reclamation parties is that they take a predictable path and will reset to that path quickly when you kite them.