Its a tricky one Phsyco, I feel for you.
From what I've read I think you might struggle getting them to sell, if the owners don't want to be contacted.
It sounds like owner, landlords and tenants. only care about themselves and their own position, which unfortunately is not surprising these days.
So IMO you need to dangle a carrot to one of them to get a resolution, your on the right track with buying the house hopefully you can find a way to make it happen.
In the interim I found this also:
https://www.legalaid.vic.gov.au/find...ith-neighbours
If a dispute with a neighbour makes you fear for your safety
If a dispute with a neighbour escalates and you fear for your safety there are laws to protect you. You can get a personal safety intervention order if:
•you have been assaulted, harassed or threatened
•your property is damaged.
What you can do
You can apply for a personal safety intervention order at any Magistrates’ Court in Victoria. However, if you have a non-violent dispute, the court will encourage you to try mediation. For more information about how to apply see Personal safety intervention orders.