The first thing I would check would be to make sure that you're both entering the same RES/ring (I know, that's a "captain obvious" statement, but thanks for humoring me

). Some planets have upwards of five or six different RES sites...some have only one.
Once you're certain of that, and if you're already in a wing and STILL can't see each other. Figure out if you can see each other in Supercruise in the same system, if you can, it's as simple as following your wingman's wake, or having him turn on his/her wing beacon to give you something to aim at. If you're both in a wing, and in the same system, and in super cruise and you CAN'T see each other on your sensors (but are still near enough that it should be possible) then one or both of you should probably try restarting the game. This isn't exactly an issue that is all that widespread (in my experience) so I'm sorry that it's turned into such a frustrating ordeal for you :/
It's always a pain when playing with friends gets bogged down or made complicated, regardless of the reasons. Especially in a group like Mobius.
I'm sending happy good luck vibes your direction, though!