How are seniors with oxygen machines able to travel to visit relatives at high altitudes?

See pulmonologist. Anyone with chronic lung disease or problems who is on oxygen should work with their pulmonoligist (lung doctor) to determine whether they can travel to altitude. It will depend upon many factors including the underlying problem, how high the inteneded travel is, and how much oxygen is need at low altitude. Some may just need an increase in oxygen, some may not be able to go.