Humans like to keep their stuff. You know, the classical scifi deal "no other species fight like humans when they're on the verge of exctinction" thinguy. Besides, I don't think it would be technocally possible, anyway: by that time, they don't have such a large fleet that they could save more than 1/100 of all mankind, they don't have FTL stuff ( the Vodians would give them theirs, but adapting them to terran ships, building them, etc, would be too long ). And they don't want Earth and Mars to be destroyed, that's their only inhabited planets ( since they never left Sol anyway ).
The aliens are all carbon-based. The grays are way more advanced than the Vodians and Terrans. The Vodians are at the same technological level, but they followed a different evolution, they were already a space faring species by then ( but didn't have FTL stuff either ). A vodian ship looks more hightech than a terran ship, but in fact it is at the same level, it just works differently. For exemple, Vodians don't know powder, and Grays never considered it would be useful to them ( they know about it, tho, coz they've seen it on Earth ). Vodians don't use metal either, btw, they use some kind of resin they take from the trees hat grow on their planet. The grays use some odd plastic. Both the grays and Vodians use energy weapons and shields, which makes them more balanced against each other. Shields can't be adapted on Terran ships because they're made with metal.
shields are very effective against energy based weapons, but absolutely useless against projectiles that will simply go through them. Ammo based weapons are also more efficent against Vodians and Gray ships, coz they break the resin/plastic, creating large hull breaches, with big hull chunks flying away. Energy weapons, on the other hand, melt metal like there's no tommorrow, so Terran ships are quite fragile to them. The grays use antigrav tech, while the Vodians use grav tech ( works the other way around, one pushes, the other one pulls ). The Vodian grav wells have some drawbacks, for exemple they generates massive amounts of heat.
The Mycoids don't really use technology, but they can learn from it and understand it. They just need the concepts, then they grow symbiots or stuff that will achieve the same result as a machine. Sometime they hijack stuff, tho.