I am by no means an expert, but I may have an idea. If the static meshes you’re grouping are in the level at start, you should be able to go into the world outliner, select the actors/meshes in there you want to group, and right click over one of the selected objects. In the drop down menu there is an option for grouping. I’ve not played with this myself, so I can’t promise this is right for you, but it seems like a good start. Click link for documentation.
And here’s the option in the menu I’m referring to:
