You can use the same jumpers. Some will put both of the jumpers in place between the 2 6V batts. If they are red & black it's a visual reminder they connect neg & pos terminals.
If you ever want or need to switch back to 12V for any reason you have enough cables to do it that way.
6V GCs are the way to go for house use.
It's not whether they are 2, 6, or 12V it's that GC batts are made different and serve much better for house use.
Read thru this link for a very good summary of deep cycle batty
Also lots of other great electrical info from a knowledgable source.