How can I maintain contact with mobile person

[Steve]

My retreat is 300 miles from where my sons and their families live, there may come a time when they need to make that trip in difficult conditions, perhaps with limited fuel or with vehicles blocking roads. I would like to keep track of their progress in case I have to meet them half way to help them in.

How would you keep in touch ? Comms will need to work at every point in the 300 mile trip, not necessarily whilst mobile so a big aerial is acceptable as long as it can be collapsed for transport.