Your question sounds like you are already running the git version of DoC. In that case, I suggest you also clone the separate repositories for Blue Marble and VD (in case you want that, see below) simply next to the mod directory in Beyond the Sword/Mods. You will find a BlueMarble.fpk file in its folder, you can then just copy it into RFC Dawn of Civilisation/Assets/.
For Varietas Delectat, you have to know that the module is currently compatible with the main mod, but it is common for that to change while the base mod is being developed. Also, when you install VD, it will overwrite some existing files of the base mod. That means that if you want to get updates affecting these files through git, there will be a conflict and the update will fail, in a way that is not easy to resolve for you. Essentially installing VD for a git version, even when compatible, will prevent further updates and defeat the purpose of running from git. If you still want to do it, copy the Assets folder from the VD git repo you cloned into RFC Dawn of Civilisation, integrating it into the existing Assets folder (overwrite everything).
But in that case, just downloading the installer to get DoC with VD is the safer and easier approach.