My husband is going to join a bank in Hongkong on employment visa. I and our kids will join him on dependent visa. His mum is old above 70 yrs and does not have her husband and my husband is only child so she can't stay alone in India. We understand she has to visit HK on visitor visa. what is the maximum period can she get at one go? When her visa expires can we request for extension immediately without any waiting period?