Nobody so far has mentioned that you reread your cross-lease agreement. What does the agreement state about insurance? IMO, that agreement comes before an outside insurance company "imposes their will" on the block of 6 flats.
Take that agreement to a lawyer and get both a modern interpretation and what was implied / assumed at the time of writing the document.
FYI My cross-lease agreement is older than me & has zero amendments. YMMV
