Originally Posted by fishboat

I can't speak to the sharing aspect(seeing each other's location), but

1) If you expect to have a cell service signal during your ride, then
a) Plan your route in some route planning software (I use RWGPS mostly)
b) Extract a GPX format file of the route
c) Go to your Google Drive>NEW>More>My Google Maps
d) Import GPX file into a map
e) Name the map
f) Set sharing to "anyone with the link"
g) You now should have your route accessible on your phone and your location will be shown
h) It may be possible to save this map-route as an "offline google map" for use without cell service..I haven't tried it

2) If you don't expect to have a cell phone signal during your ride, then
i) Do 1a above
j) Extract a KML file of your route. Name it with your route name, i.e. "Katy Trail"
k) Download and install the app Maps.Me.
l) Download the states and large cities you'll be in from within Maps.Me
m) Email the KML file from j) above to yourself
n) On your phone, open the email & KML file. If your phone has Google Earth on it, you may get a popup asking which app should open the KML file (Google Earth or Maps.Me, choose Maps.Me)
o) You'll now have an offline map and route available in Maps.Me and your location will be shown. Tap the Star on the bottom of your open Maps.Me app(second from right) and you'll see the Bookmarks page..turn the route on and off with the check box in front of you route.
p) Again..no idea on sharing..though the KML file can be emailed to a friend and they can load the same setup you've just done.

Personal preference..but I don't use my phone for navigation(though have things loaded so it can serve as a backup) as it's safer to use a dedicated GPS device. The phone (for me) is more of a communication and safety device. If I crash somewhere and need help, I don't want my phone low on power due to using it for navigation.