Pets are great friends to a human being. Having a dog is surely the wisest decision as dogs are always faithful to their owners/parents and tend to get attached easily. Having said that, fifty is not old age. But since you mentioned that there will be a trainer and sitter - there is as such no problem to keep a dog. Older people need a dog who is less active as they cannot run around their little dog all day as they are reaching a phase where they need rest.
Older people love going on walks but having an energetic dog will make them run which is not too good for their health. Never get a pup for an elderly couple as pups need to play all day long and taking care of them is a concern. Older dogs such as a senior great dane can be a great dog for older people. They usually give out a very calm and friendly vibe. Sometimes dogs become a reason for our joy - a reason for our living. A poodle is another option as it is a very elite dog which is friendly and not too active like others.
A pug can also be a great company for elders as they are very chirpy but lazy. Lhasa Apso loves elderly people which can be a great gift as they look amazing too. And yes, a lawn and pool is what every dog wants. So, don't think twice - adopt or buy a new member for the elderly parents.
