Your rights are that due to a defect in the common property you no longer have a bathroom, therefore they have to pay to have it replaced.
You are also entitled to the costs associated with your tenants.
That is because your loss was caused by the fault in the common property.
It sounds like it is too late but you should have sorted this out with them before they ripped out the bathroom.
They should check with the strata insurer as to whether the insurance covers it.