It's about stamp duty of HK taxation

= 1. Mr. Zack Zhang got married in the month April 2019. His father, Mr. Adam Zhang, transferred to him at no consideration as a marriage gift 40,000 shares of Bank of China (stock code 3988) by end of March 2017 when the market price was $3.5 per share. In March 2020, Mr. Adam Zhang transferred 60,000 shares to Mr. Zack Zhang again to celebrate latter's marriage for one year and the birth of a son, Mr. Bobby Zhang. The market price was $3 per share. You are required to inform Mr. Adam Zhang and Mr. Zack Zhang if they were subject to stamp duty for these two transactions. If yes, under what Head and the amount of stamp duty they had to pay. If not, what procedures they had to follow before they were exempt. 2. Ms. Huang is an estate agent for a few years. Recently, she noticed the followings occurred to two of her clients: Client A: A retired person living with his wife. Their children were all grown up and had their own families. Client A considered his current home of 1,000 sq. ft. too large and wanted to buy a smaller flat of 600 sq. ft. His current home had a market value $8 million. Client B: B's wife just gave birth to a daughter. They already had a son aged 3. B considered his current flat of 600 sq. ft. small as his mother was living with them and there was a Philippine maid. The market price of his current flat was $5 million. He targeted to buy a larger flat of 1,000 sq. ft. around $8 million [Note: Both clients did not own other properties and were HK permanent residents.] Ms. Huang asked your opinion on the stamp duty issue: (a) if Client A and Client B would buy the other's property at market value, (b) if both parties swap their properties; (e) what actions are required for (b)