My sibling is in the process of their house being built and is a first time home buyer, this is in Western Australia. Before the house plans were finalised they visited the builders display home and asked for several changes to the base house so that it matched the build and style of the display home. When they asked for certain features to be modified the builders said the feature would cost however many thousands of dollars and then later charge extra so the final cost for the change would usually be double what was told to them. They asked for several features to match the display home for example the ceiling or roof design, when they did this they said how much it would cost and said the ceiling design was called X design and wrote X design on the building plans.
However they are now saying that X design is not the same as the one in the display home, when they specifically asked for “the same as the display home” and wrote X design after they asked for the design showed to them. This happened for several features of the house and it is currently being built, it seems to me they charged extra and then even more after saying the features would cost more and then are using jargon unknown to someone outside the house building industry in an attempt to not provide the features paid for.
As the house is being built now, several features were already built with the inferior basic version and they are trying as hard as they can to not provide the features paid for. The house that is supposed to be being built cost approximately double of what the base house plan cost and it seems intent they are intent in not providing the upgrades paid for as several of them are already missing, wrong or are using the inferior options.
What can I do to help them, is there any steps they can take and is the home builders conduct illegal?
Edit: I should add that this is taking place in Western Australia
What does the contract say? I think you're not getting the full story, while builders can be dodgy, this doesn't sound right