I have a fascination with plotting routes with Teslas to see how they would work. But I find something common on these forums that is frustrating. New owners come asking about, "Can this work?" checking on some nail-biting tight distance when they are intentionally skipping over Superchargers. If it's potentially tight, don't skip them, and take a quick 10-15 minute break to make it easy.
317 miles would work in summer for the 225 mile leg to Ogalalla SC, arriving with 29% if he started at 100%.
I just looked at that route, and you are driving right by the Supercharger in Brush, CO. It's halfway. Just use it.
The second leg is 216 miles to FIL's home, with no charging stations along the way, so he might arrive with about 10% if he supercharged to 80% at Ogalalla.
You never mentioned a specific city, and I see dozens of places listed as "Sand Hills" in Nebraska, so hard to say where this second leg of the route even is. But I noticed you mentioned the term as "charging stations". People new to electric cars are sometimes hung up on that idea that they need a "filling station" for electric vehicles. But these cars can charge from just about any source of AC electricity, which every building has. So the other thing is that in rural areas that generally might not have big cities enough to have "charging stations", that means they frequently have campgrounds and RV parks. (Although, yes, I realize that's more a thing in scenic places with hiking and such, rather than flat Nebraska.) I've charged at RV parks before, so that may be another possibility if you can spare an hour for a lunch stop to add an extra 30-40 miles into your battery along the way.
You can check Plugshare for all kinds of charging options, although it is pretty sparse there. And sites like Allstays.com or RVParky.com show campgrounds that would have electrical hookups.
