xray
P85 6313 - X Res 3450
You will probably get more answers if you post your question in a different thread. You should first try entering your itinerary in EVTripPlanner or whatever that website is called. It will tell you how many kWh it will normally take for your trip, excluding wind. With a fully loaded car, and gaining 2,000 feet in elevation, I would think it's highly unlikely you'd be able to do 260 miles on a single charge unless you really hyper-miled it, meaning drove 55 mph the whole way. I would think you'd need to stop someplace to pick up at least 20 rated miles.
On a more general level, I think you should have a talk with your family about what to expect road tripping with the MS and how it might take longer, make a few more stops, but you're going to enjoy yourselves and not be rushing. If they can't accept that, I would either take a different car, find a place to stop overnight, or fly.
Completely agree, when it comes to roadtrip planning EVTripPlanner.com is invaluable. It takes into account many factors that are not apparent when only looking at distance on a map. Highly recommend it.