https://mypt3.com/i-miliki

Based on the article there will be a new home owner will enjoy different stamp duty based the amount of home.

If a couple joint name and buy, one new home owner but own had a joint name Propety with his family. How does this situation play out for this exemption? Any expert here ?

This new stamp duty exemption is just an announcement. Not "valid" until and unless it is officially gazetted and become law.

For the joint buyer scenario, only can get half exemption. For example, AB jointly buy a house. A = first house. B = second house. Only A get exemption. B need to pay full.