There is a two edged sword in here.
NBN installation will apply to all lot owners. Whatever they deem suitable for you, the other owners will need to also comply with.
I can understand how the other lot owners feel, and maybe you have contravened the by laws.
The correspondence concerning NBN installations that I have seen does make it clear that OC permission may be needed in some cases. NBN is being upfront about this.
Perhaps a meeting of all owners to discuss how NBN is to be installed could be first call. All owners will probably need a by law so why not agree on one bylaw covering all lots rather than having 8 separate bylaws.
Consider also that an NBN is pretty much mandated as your regular phone lines will disappear.