Air Asia are a point to point lo cost carrier. They do not sell connecting flights. Even if your relatives have both flights on the same ticket, they can only be booked seperatly, constituting two seperate independent contracts, STN-KUL and then KUL-PER. I'm afraid that legally Air Asia are in the right.
Morally however I agree that this is unjust, especially for an airline which markets itself as a low cost alternative on the 'kangeroo route' from Europe to Oz. My advice to you would be to calmly appeal to their sense of reason. Having flown short haul with Air Asia I know that as a company they are more 'human' than a lot of their European peers. Failing that check your rights under the EU air passengers charter. If they have changed their flight times significantly so close to the departure date they will be entitled to some form of compensation.
Good luck!
Anansis.
P.s. 16,000 Malaysian Ringits is around £3000- are you sure its not 1600 (£300)? That would seem more realistic.