To assemble a Rumba animation project, you will have first to export each Maya character rig using mtorba to get a .rumbanode file.
You may also need some alembic files with the static scene elements.
Once exported, reference each character and the alembic files in Rumba using File -> Reference Nodes…
You can also do this in Python, see Reference a file.
Once the animation is done, you will have to export it to your preferred DCC. There is two possible workflows.
Export a geometry cache¶
In the first one, you can export an alembic file with all the character geometry baked.