Thanks! Yes I looked into these. There are other options that also provide a ton of assets etc to speed up development as well. But thanks for breaking it down. The photon plugin might be a good option but I don't mind if we need to invest in another framework to speed things up. I don't think it will take that long once we have the time to work on it properly. It'll be huge

A big question is what language the other coders are familiar with. Out of all of these, Unity is the most versatile language-wise as it accepts scripts in C#, its own custom script, JavaScript and C++. So even if you another were working on the same module, you could be using two different languages and Unity would automatically convert them on the game build. You can also use LUA, but I think that needs an external addon. I know that the other two, UDK and Gamebryo are often used with LUA. UDK goes with C++ and its own custom scripting, and I'm not sure Gamebryo's language.
FWIW, there are a lot of options. But these are the three most commonly used so I figure there's a reason for it (and it also means there's more than abundant support).
I am fine with any language, although I will admit that I am leaning towards C# or JavaScript. Any engine is fine for me as well. I think Unity is attractive and easy for beginners. Let's start the game already! We should get all interested parties and finalize the GDD and the important modules to code up. I can also do a bit of digital painting as well hehe. Not super well, but it's w/e.

Unfortunately, I have a lot on my plate. HYPERfuture, you should set up a schedule to get this started! Will this be built in-house or are you planning to outsource to an indie studio or something?