hikvision remote veiwing

Hi,soo,im in a bit of a pickle,my husband and brother in law have installed a hikvision system for a customer,my BIL does all the techy side of it,the customer had no internet at the time but now has,my BIL has gone awol and im trying to work out how to do the techy side myself! Your videos are so helpful,what im trying to work out is how our customers son can view his mothers cameras remotely,i understand i have to do port forwarding? can this be just for the DVR or do i have to open a port...

hikvision remote veiwing