8S2P means you have two cells in parallel. That just means you have two cells side by side, like you have in the drawing, electrically connected, so… you’re parallel connections are always symmetrical where as polarity is concerned. Your series connections always go positive to negative, your drawing isn’t right at all. You really need to do your due diligence in research if you want to build batteries- it’s incredibly dangerous. Lithium ion cells have more energy in them per gram than dynamite.
Don’t you think you should know all of this stuff before you go building it? It’s all available on Google, and very easy to find. I’m not going to help you any further because you could burn down your house, or worse.