Visa for Malaysians to enter Hong Kong, Macau, Shenzhen

Hello, I'd like to bring my parents for a 1 week holiday in Hong Kong, Macau and Shenzhen in December. They are Malaysians and are staying in Johor, and we'd be leaving from Singapore. What type of visa would they need, and can I apply for it in Singapore ? I'm a Singaporean, and i understand that I would not need a visa for entry into the 3 cities for the 1 week stay, is this correct ? Appreciate any advice you can give. Thank you.