i think its terrible that there isnt a Huge industrial push for female product to remedy this void (no pun).
There are actually many products out there for females who need to stand up while urinating(links below) . ! thing I use is the trusty GPS, it will find all the places to pee with "points of interest". Dont chug down 40 oz of water when you are 50 miles away from a place to pee on the GPS. If you need water , eat something salty , it will help your body retain the water in your muscles.
your questions:1 anywhere out of sight and safe, take turns , make sure you know where you bff is and vise versa .
2 . Steal a hunk of napkins or ask at any fastfood/gasstop , stick them under the tire b4 driving off, or feed it to the dirt.
3. You certainly get less splash in the weeds . Be Careful, 2 girls traveling alone,pulling their pants down in public is a invitation to wandering Cocksmen . Keep the bearspray handy even while peeing =D