If you mean the actual content of the text messages, the easiest way would be to look on the individual devices. Other than that, you would have to log in to each of the individual MyVerizon accounts of each line on the account separately to view the content online. To log in to each account, you would have to get the userid and password from each line's user assuming they have actually set up a MyVerizon account for the line. If they haven't set up an online MyVerizon account, you would have to have the device active on that line to enter in the one time code which would be sent to the device in order to set up a new account.
Then you would be able to log in to the online MyVerizon account but would have to log out of that account and do the same thing for each line. There is no way to view the content for each line in one central location or one master account.