GitHub can be used for anything, not exclusively C++. However, it can only merge text files, so it’s still possible to have conflicts with blueprint files when multiple programmers are editing the same file at the same time. Github only has a 1GB limit though, which depending on your drawing style may be way to small (which I assume is the case since you complain about huge files).
If you will work from a distance, then you will need some way to send files to eachother.
If storage is the main problem, then someone needs to have a computer turned on all the time which either hosts a git/other cloud syncing server or which has a drive opened to the network (in which case, don’t forget to password-protect it, since there are many people scanning random ip’s for running connections like that). Also I think that a free Mega account can hold 50GB, which should be enough for a game made by 5 people if you only put 1 project on there at the same time, but since I never used it, I’m not 100% sure of this limit. Onedrive allows up to 1TB if you have an office 365 license, but their sharing system used to not even support syncing shared folders, so if they haven’t added that yet, it’s quite useless.
If internet speeds and/or data limits are the problem, then you either only sync what’s nessicary (let everyone have his own UE project where he/she works on his/her own parts, and send only the needed files to eachother, when optionally merging the projects at regular intervals), or make sure the files aren’t huge. Usually, the code of a game is pretty small, and assets like models, textures and movie files are which makes it so big. You can easily downscale textures and mess with the compression to reduce their file size by a lot, and you should b able to make models a lot less detailed using simple scripts. Then only whoever created the assets needs to keep the high-detail versions and everyone else can work with the smaller low-res versions, untill you finally merge everything at the end (or at regular intervals).
Personally, I use a self-hosted Git server, and I use a low-poly stylized drawing style so that the file size of my assets is quite low.