1 story, cbs, do the sistered joists need support?
I am very confused by your post. First off, most support walls are built using single studs spaced approximately 16 inches on center. I do not understand what you mean by a "2x4 combo beam". If you are referring to double studs, they are not called combo studs, and double studs are not beams, and you do not need double studs in a load bearing wall.
Then you mention that you have sistered 2x6x12 foot beams in the attic. Do you mean that you have attic floor joists perpendicular to your wall? And exactly what do you mean by sistered? Possibly you are referring to floor joists which overlap your wall, and are nailed together. From the description, you may have conventional floor joists supported by the wall, which would make the wall a load bearing wall. Best to post some pictures, maybe a scaled diagram of what you have.
Finally you mention that your walls are CBS. I am not familiar with the term CBS as a structural term, there is a television network called CBS, but not sure what you are referring to. Anyway, post some pictures, and make sure in your descriptions that you are using correct terminology for the structural elements in your house. Vertical supports in the wall are called studs, rafters typically support the roof, joists support floors, and beams are typically large lumber that support joists.