@ManGar,
I have an S1/S2 setup side-by-side on my Home WiFi network - you can have multiple systems, even if they are all S2, or all S1, or a combination of both.
Just do not take the upgrade path to create an S2 system from an S1 system, because they both then end up with the same Sonos Household ID and can get entangled (similar to what you are describing in your post).
A good ‘rule of thumb’ is to create a brand new system using a ‘reset’ Sonos App - note I use the word ‘reset’ rather than a newly installed App, as that can make a difference too for first time use/creation of a system.
If using two, or more, S1 or S2 Sonos systems - then I recommend using a different Sonos controller device, but for a single S1 and a single S2 system, then the same controller device will be fine.