Fellow cruisers, I believe the OP asked for recommendations on the best walkie talkie to stay in touch with their Dad's caregiver. Now that I am also in the position of wanting/needing to be able to contact my travel partner should we get separated on the ship, I too would like the information. Sometimes, something as simple as a bathroom visit can lead to a person getting disoriented and subsequently lost on the ship. It is uncomfortable and frightening for the lost person and their companion. If you haven't experienced it, then you can not possibly understand.
I have no intentions of disturbing my fellow cruisers with the constant "can you hear me now," conversation, but I would like to know if there is a set of walkie talkies that will offer a possible solution. Yes, I have tried the ship's app and I can tell you from experience that it is ship and cruise line specific whether it works or not -- regardless of whether you buy the ship's wi-fi. It is not a guarantee that the app will work nor that it will work well. My experience with the Princess app was favorable, my experience with the Royal Caribbean app was horrible (and I love Royal - I'm Diamond Plus, knocking on Pinnacle's door).
If you have a walkie talkie recommendation, please share it. If not, please just keep scrolling -- no commentary needed. Thanks and happy sailing to all of you!