I’m not sure if your buttons are supposed to work that way! Can you give a link, where you bought them and maybe there can be found any document with further information.
Many TonUINOs come with a powerbank-solution. So, no problem with that!
Maybe this thread https://discourse.voss.earth/t/an-und-ausschalter-anbringen/14673
can give you any hints. Even though it is in german, i’m sure you can find a way on the internet to translate 