1. Helghan & Vekta (Killzone) + The Alliance & Browncoats (Firefly) + Colonial Marines/Earth (Aliens) + 12 Colonies + Cylons (nBSG) V's The Covenant
2. The Location is a neutral galaxy (All assets taken over eg shipyards, orbital infrastructure etc. Allies assets are all in a sphere 80LY wide. No Covenant facilities in that 80LY.
3. Victory Conditions- Covenat to kill the humans like OTL. The Alliance to survive for 5 years as a functioning society at around the same level as when they entered.
4. Battle Prerequisites- The Covenant know nothing about their opponents apart from being human. The Allies have 10 years prep time, tech sharing and have the general structure of the Covenant government and society. The Covenant believe (in some cases there is) a holy relic on all primary worlds the Allies occupy so wont go straight for glassing.
Thematically it could be fun.
With the Alliance/Browncoats, they live in a small star cluster of five stars and seven brown dwarfs with over sixty or so Earth style planets spinning around. So it appears pretty densely populated. The Twelve Colonies meanwhile are almost literally all in the same star system, and almost all of the planets are heavily populated to the billions and had a very large (for their size) industrial capacity. Plus the Cylons. I never played Killzone so I can't speculate on that and my knowledge of the AvP setting with the Colonial Marines is pretty hazy, but their canon policy is just as hazy so...
This eighty light year across area of them sounds like it could actually contain all of them. I'm not too big a fan of tech sharing in general since it can easily lead into weird ASB territory but the fact they can use nBSG Hyperdrive to get around FTL wise would be nice.
I guess I'd envision the three civilization in that the Alliance and Twelve Colonies and the AvP polities as their own thing. The Twelve Colonies obviously developed independently (Ancient Human Aliens like we see in Stargate) and the Alliance might've been emigres from the AvPverse Humanity and so the AvPverse Humanity despite being the origin of Humans doesn't neccessarily mean they are the most developed polity.
The Twelve Colonies and their Cylon buddies would likely be the resource base. Those Twelve worlds alone maintained a fleet of 120 Battlestars and thousands of smaller ships and dozens of squadrons of Raptors and Vipers and this was in spite of a peace dividend of almost an entire generation. The Cylons meanwhile had a seemingly smaller but still sizable military industrial capacity (and could very likely devote more of their resources to it) so the Twelve Colonies would seem to be the industrial core and maybe economic core of this Alliance.
Between the two of them they could probably field a few
hundred capital grade warships perhaps if they shifted more resources to a military stance.
The United Americas (apparently that's the name of the Colonial Marines overall polity) and megacorporations like Weyland-Yutani meanwhile despite being the home of Earth, would likely be the ones who control the idea of pushing out to the edges of their little part of the galaxy. They'll be the ones sending out the colonists into the great unknown, expanding the frontier and with their self sufficient, heavily automated and highly trained and professional Colonial Marine Corps, be able to set up all of the frontier and border areas for development and along with being scouts and recon and a military force, can start shipping resources back to the industrial heart of the Low-Tiers which would likely include the Sol System and other larger colonies they might possess and which likely possess quite an impressive industrial and economic base as well but the Twelve Colonies and Alliance as well.
The Universal Alliance meanwhile seems a far bit less dense militarily then the other groups. Twelve systems and sixty Earths plus loads of habitable moons and everything and the Alliance outside of the Core seems to have a very light touch, but those Core Worlds are highly developed as we can see with advanced modern technology and big urban centers at the very least. But they could still be militarily challenged or threatened by a potential Independent/Browncoat threat which makes me think they aren't a military powerhouse. They do have some capacity, a strong intelligence network and some quirky research projects and highly capable individuals. But they'd seem to be the 'weakest' main faction of the three.
The Browncoats/Independents would likely be useful as well, but it'd be as a support. Special Operations. Supporting frontier operation. Smuggling. Trade. Information broking. Counter-intelligence and espionage. Plus they'd be a glue and a lubricant of a social fabric between all of the factions involved. Their independent streak means that in the Low Tier Alliance they could work with everyone even if its through black markets and back channels instead of officially.
Beyond Hyperdrives, the only other tech sharing that might be needed is in ship to ship weapons. The Colonial Navy uses heavy guns (like you see on Pegasus) and loads of flak style cannons (which you see everywhere) and has the capability to launch nuclear missiles. The Cylons love using nuclear missile launchers and has some EW capability.
The Alliance/Browncoats apparently have lots of autocannons of indeterminate origin, some of the vessels like the Longbow-class Patrol Cruisers are also giant space cannons but also according the the RPG many of their ships have banks of hundreds and hundreds of missiles and not just exploding ones, but decoy missiles as well.
And the poor Colonial Marines, from what limitedness we've seen, uses lasers for missile interception and the Conestoga-class main anti-ship weapon is a mere eight anti-starship missiles which look cool but seem wholly inadequate to go up against the Covenant. That'll be needing an upgrade.
The main benefit of the Low Tier Alliance is that the Cylons/Twelve Colonies can probably pump out the big warships while the United Alliance and United Americas can churn out loads of smaller ships, variations of space cannon type of vessels and ones that act like missile boats. The UNSC's main weapon before using MAC Cannons and SMAC cannons and variations thereof was launching Archer Missiles which wasn't a great option, but still somewhat effective against the Covenant. The Low Tier Alliance could do missile spam pretty well it seems, but is way behind on the big cannons to blow away the enemy. The newer Battletars have big guns, and the Alliance uses big guns on some of their ships, so that could be brought to bear to swat at Covenant vessels but it just doesn't seem to be on the same level.
Ideally they'd be launching missile spams, pegging away with heavy guns and using their scads of fighters, bombers, raiders and attack aircraft simultaneously to overwhelm the filthy alien menaces.
In regards to a 'Cole Protocol' that seems like something that would be up the alley of the Cylons because if the Covenant finds them towards the onset, it just might be ggwp because the Low Tier Alliance just doesn't seem to have the strategic depth.