JimC

If everyone has a cell phone, I recommend they all download the Royal App.  It makes it easier to upload vaccination cards, scan passports, etc. even if you initially check them by name just to get a time slot.  

I can see where I have linked the two reservations on royalcaribbean.com. On my app I only see my reservation. Is it possible to add another reservation to my app and how do I do it? Or do I just sign on to royalcaribbean.com whenever I want to work with the linked reservations. Thanks

Any separate reservations can be linked as long as you have their sailing number and DOB. We sail sometimes with my wife's two best friends and we will link our accounts as they know how diligent my wife is on check in, reservations, boarding times, etc. We all coordinate our schedules but at the beginning they let us do the sign in as they know my wife will be up at midnight on check in day to get the earliest boarding time.

I was linked with my adult sons reservation. I was able to do his arrival time.  I was also able to do the healthy sail portion (which opens after NOON the day before the cruise sails) 
I could also do reservations in the app with them when on board 
precruise I could select them to add to any reservation I made.
each person can go to royalcarribean.com and create an account and add their reservation number to their new account. It should then show in the app. If your reservation is not showing as linked to theirs they can add your reservation number. (Link missing reservation)  it is wise they each use their own email address so they will get updated and the post cruise survey.
They can also call Crown and anchor (C&A) and sign up for a loyalty number though I hear sometimes they say you need to complete the cruise first to get the number  1 (800) 526-9723  they should have their reservation # handy.
 

If the other guests have the reservation number, they should have no problem signing in on the Royal app.

This is the first RCL cruise I have done that is not Solo.  I made sure my son has a Crown and Anchor number and RCL account.  Then I checked him in and did part of his check in.  He then went in and finished his check-in.  He could have done the entire thing himself.  Also, when he signs in online, he has the ability to book excursions for himself.  Their information is already on the reservation number so they should be able to do everything themself based on the reservation number.  Depending on the ages it is easier if everyone has the RCL App on their phones and does their own wellness check in.  They will want the app to do their planning and check the cruise planner.  In the past we carried a paper around that had all the activities on it but now most people just carry their cell phone and do everything on the RCL app.
Last note:  Make sure everyone knows to put their phones on airplane mode during the cruise.