Making one ceiling light circuit into multiple light circuits with fibaro dimmer 2 switches

First of all, Congrats on making the very clear drawings,

Please read: WARNING: Electrical Safety is Paramount (Risks: Shock, Fire, Death by electrocution)

First What I see is they installed the wrong color wires, (if the Colors are correct in the drawing)
Only the incoming Live Wire (normally marked as L) in your first drawing on L2 dashed incoming from the Fuse box should be brown, all other Brown wires in the drawing should be Black. in that case is is a verry classic Multiway switching (in Dutch Hotelschakeling)

But seeing the colors (ignoring what you specify as Contacts) it is almost a Alternate Dutch alternatief
(But then the Contact don’t match your drawing)

Therefore it is not enough that you think the first is the current situation… Verify it, and work safe!

The good news, the Second drawing looks good, and would they have used Black wires where they should have been correct, you had to change them to brown… now these are already brown (in your drawing).