Venus’s atmosphere is 100x denser than earth’s, so you could just seal the metal balloons at sea level pressure and it wouldn’t really make a difference. Or you could seal them in a vacuum on earth. Not sure why you would need to feel them in space.
Don't we want them to be rigid spheres?
And what weighs more - the air that got trapped in the sphere when we made it, or the machine we sent up to space to assemble a sphere there?
Cold weld it in space, it's not that difficult with some engineering.
Space X?
This is pretty well guaranteed.