Alright folks, hang onto your poopsocks because this mission is going to be a long, grueling pain in the ass. In this fight you are fighting the infamous Stronghold quartet; Rat, Snake, Pig and Wolf, fighting over a mass of iron and stone in the middle of the map, and to kick it all off, they each have 4000gp to your 2000.
The trick here is we need to get the element of surprise on these guys quickly if we are to control the resources in the center and defend ourselves by any means. We also need to prevent our enemies from completely raping us with all they can bring to bear. So this is what we're going to have to do. I recommend setting game speed to 20, and even using the 'P' pause button or Esc key between actions to keep calm and quick.
Place your Trading Post, Granary (1/2 rations), Armory, one hovel and buy in 50 stone. There are two entryways onto the middle island; one from the east and one forking path to the south. Beside the eastern entrance, place two towers and connect them with stone and stairs. Place an Engineer's Guild and Barracks. Buy in 15 bows and recruit all 15 as well as four engineers. Place a ballista on the left tower, a mongonel on the right. Get everyone up there and have the mangonel continually shell the Rat's keep or gatehouse. Destroy the bottom stair step so no one can get to you. Let the ballista fire at what it wants, and do NOT place braziers as you want to protect your own quarries/mines.
Place a single quarry and three tethers as far east as possible. You can place an iron mine, but in my experience it kept getting blown up. Place two Apple Farms, and a handful of woodcutters. Buy 5 Hops, place a brewery and inn (this will mitigate low rations). Use the rest of your stone to create a thick wall across the other two fords to the west so nothing can reach you (without a struggle), maybe buy in another 5 or 10 if you can afford it. With your final few scraps of coin, you might want to place more farms, build a fletcher or two, or construct a mercenary outpost and some slingers.
It will take a long while before you start to get stone back to sell, and wood isn't very plentiful without your guys crossing the river. When you can I suggest you either build fletchers, place a diary farm or two with some tanners, or make a hops farm so you don't have to buy in hops. Before long the Pig will start to rush you with crossbows, macemen, even catapults so I suggest on your western wall you place a sentry tower or two, manning them with archers and crossbowmen as they come. All in all though, I suggest you not sell anything too rashly; you may need stone for quick repairs, or coin for some quick mercenaries.
--IN CASE OF EMERGENCY--
Several terrible things can happen to you in the first few minutes. These are what happened (or almost happened) to me and how I reacted.
-Pig rushed me with macemen before I could build sentry towers, bashed through the walls and starting causing havoc. I placed a mercenary post and bought what meager force of slingers I could to fend them off. Preventative measure would be to place a couple sentry towers facing west filled with archers and crossbowmen. Better yet, place a larger tower with a ballista in case Pig or Wolf build catapults (which they did and almost destroyed everything again.
-The Snake will attempt to throw slaves at your quarry constantly. You may want to place a Water Pot nearby, otherwise load your northern towers with a bunch of guys. Make sure your ballista is going strong and your mangonel keeps firing on the Rat to cripple him.
-If the Pig and Wolf start building catapults to hammer your defenses like they did to me, you may need to send a suicide force of archers to murder the catapults. Try to repair any towers before they're fully destroyed.
-In the face of a massive horde of Wolf pikemen and swordsmen, spawn as many crossbowmen as you can and get them on top of any towers or elevation you can. Be sure to destroy the bottom stair steps of any towers when you're not placing new things on them; a single handful of macemen or swordsmen can murder everything you have if you let it.
The Wolf is going to use his eastern mangonel to constantly shell your quarry and any other quarries you hope to build. I built two trebuchets on my side of the ford to destroy that tower, then quickly placed two touching square towers. I send all my built up archers and crossbowmen there and placed a mangonel on each one to constantly shell that location and his ballista tower otherwise. Only then was I able to clear out the rest of the resource island with arabian swords and place as many quarries as I could to rake in the stone money. I had to babysit those mangonels a lot to make sure they kept shelling his; you do the same and you won't see your things destroyed.
Keep building up archers and crossbows and replenishing your towers; keep all your crossbowmen west, as Snake and Rat use no heavy units that require crossbows. You can even do what I did and build several more towers to the west for more mangonels and ballista for ultimate harass. Just remember to keep destroying your bottom stair step, as this harassment will make the Pig and Wolf very angry, and one or both may send giant waves of everything they have in an attempt to stop you.
How you defeat each lord is up to you, but I recommend starting with the Rat to give you some breathing room. I also recommend building some fire ballista to destroy outside buildings of all four to troll them. Once you've shelled Rat to oblivion with your mangonel a dozen or more macemen should do the trick. After he is done for, you could kill the Snake but I didn't find him very much of a threat. I started building a lot of dairy farms for leather, and buying in iron which blacksmiths turned into maces (iron being cheaper than maces to buy). A handful of trebuchets later I killed the Pig, Wolf, then Snake. Really though, once you have enough archers to repel the Snake and Rat, and one you're able to successfully shell and weather the attacks of Pig and Wolf, you'll inevitably win the day.