Me, for I'm the main modder,
....
How do I convert these into meshes?
A mod leader who ask this question simply show that something is wrong...
Any guy who wish to mod need to download the stardock/ironclad tools... i mean the Forgetools... in it, you will find the "documentation" directory, read the 3 pdf, not updated but it is the basis for modding ( one of the pdf explainthe XSI step )... for convert to .mesh, go to the directory "convertXSI )...
I advice you to visit http://soase.weebly.com/ ... the place is filled with useful information for any newbies modders...
As for the models, it is too much early for convert them to .mesh ... first, your texturer ( 2D artist ) need to explain to your modeler ( 3D artist ) how he wish to paint the model... by example, select area where there will be marking ( text )... once this know, the modeler can begin the UV optimization process ( piece with text or number cannot be optimized ) and create the new paint template...
Once the UV optimization is done, you can begin the XSI stage ( tangent, hardpoint, etc )... best is to wait that the 2D artist have done the textures... be sure before hardpointing to have think about the .entity file who will be used for call the model... need to know weapons hardpoint, hangar hardpoint, etc...
Well, i cannot explain everything... i am only a modeler who have learn a lot being a member of several mod team but who don't know enough ( yet ) for be a mod leader...
I can't post screenshots, unless you want to see a Skirantra...
You mean the NG_Skirantra

As you can see, the models have a mix of tec shape and organic shape... since your lore speak about "we took control of most of the quarantine fleet", maybe we can say that "The Darkness" race is a organic parasitic race... it will explain the strange mix of TEC and organic in their ship... in some way, very similar to the Omega or Polaris from the Babylon 5 universe who was upgraded with organic tech from the shadow...
Modeler who have already made some models for other mods can easily add some organic part to their models... and it will not be long before you have all the needed models for your mod...
Point is that you need to wrote more about the "lore"... a few lines is not enough... modeler and texturer will use the lore for make their model... i think that you need somebody able to write good story about the Darkness race in your team... well, you need plenty of people... from real 2D artist who make sketch, to people able to create music/sound to for your mod...