Jacaranda is not a native tree so unless it has some special historical significence Tree Preseveration Order would not be applicable.
Owners can cut down branches of tree overhanging their property but cannot make neighbours cut down branches of tree that are exclusively on the their property.
If the tree has been their for 100+ years it obviously was their when current parties moved in and so they have no complaint as they new the situation when they bought their nice new property.
I suspect also a special resoloution is required for a strata to pursue legal action and this requires a motion passed by 75% of the owners. As their are only 3 all need to agree to this action.