Long-distance traveling can be difficult for elderly people due to mobility issues and health complications. That is why you should plan the private transportation for them in advanced.
The best one lond distance transportation is considered to be by air, for example helicopter. But they also can use usual airlines, but make sure than flight attendant can suport them, and airline company can provide needed wheelchair and basic medical support during the flight.
I recommend you to learn more about private transportation services https://myallamericancare.com/blog/2020/10/03/private-transportation-for-seniors/ to make sure that you found out about all features of it, especially the part about insurance and accidents cover. It is also very important.