exclusive use/purchase of common property

We are a small strata of 6.  The building is surrounded by gardens, which we all enjoy.  2 units at the rear of the building have recently changed hands.  The new owners of both units want purchase and  build onto the rear garden area which is next to their balconies.  The other 4 units do not want to sell, as we all enjoy the fully landscaped gardens which surround the building, and we feel that our amenity will be diminished by such a sale.    At our last executive meeting the 2 owners of the rear units told us that if we did not accept their offer of sale, they would take us to NCAT.  They said that NCAT would more than likely rule that we  were “unreasonable” in not accepting their offer, and would make us sell to them!  Is this possible?  We are 4 are older people and we have no idea how NCAT works.   They also said that NCAT would make us sell the common area because we need to raise funds for some repairs to the building.  We are confused, as we already have all the funds we need ready for special levies to be struck for the repairs.   Is it possible to make owners sell the common property to  fund repair of common property, even though we want to do the repairs by special levies and we can fund these?