EDIT:Posted my answer here, since that was on the Construct 2 forum
I tried to make two simple projects with families and variables and merge them together. It does indeed work perfectly.
Just have to copy the files (making sure that there is no duplicate names) and edit the ".c3proj" file, adding the new objects, layouts, event sheets, families,etc on the specified lines. It is very important to put "," on every entry before the last one of a section, as it indicates that there is more "content" to be loaded.
"items": [ "Circle_Obj",
"Triangle_Obj" <- Last one
Also, using the new desktop version of C3 helped me to speed up the process, as it allows you to save projects as folders, so you don't have to ".zip" everything an change it to ".c3p" afterwards.
Now I'm trying to merge that simple project I mentioned with my main one, but no success until now.
Maybe the subfolder structures I have are making things harder.
I'll reply once I figure this out...may be helpful for lots of people.
And thanks a lot!