This is my first post so please be gentle with me :)
As to a meeting point for the run how about just off the bypass at the Lothianburn exit. There's a long stretch of road there that's easy to park on across the road from Lothianburn golf club and up to the Steading pub.
Easy to find (hopefully) for everyone & easy access to the bypass for heading to the A1.
or...
The services/Burger King at the end of the bypass. Get to the EAST end of the bypass and go straight through as if heading for Musselburgh. Turn in left about 30 yards off the roundabout. Very near my house as well
Cheers,
KenL