"It also took in Lasswade Village and the Hillhead Climb on the return leg too I think, which I wouldn't personally want to send a mass of riders down at once"
Riders are fairly well spread out by the time they get to Edinburgh. Or at least they were at the time I arrived last time.
I do remember the 'bright lights' of Edinburgh being a bit of a shock to the system after nearly 2 days of rural views/roads.
I hit the Roslin path soon after dusk and whilst enjoying the smooth path it was a little disconcerting not to be following roads, but diving under them. (In hindsight I should have reconnoitred this part).
Heading out the next morning, it was a bit fiddly getting to the familiar roads of the granites, with my first visit to Lasswade and Hillhead, but I'm not sure what other options exist.
I also don't understand making the turn at Dunfermline this time round unless they can't get an Edinburgh School which would be odd. I found it hard enough knowing I had done an extra 5 miles on day 1 due to a navigation error.
My suspicion is that they'll go Moffat, Broughton, Carnwath, Kirknewton,then Newbridge or Winchburgh, FRB on the Northbound leg. Any route coming up East of Hillend will have a right faff to get West enough for the FRB, and using the A90 path both ways is a recipe for disaster.
On the return leg, I wonder if they'll route along Queensferry High Street so you get the decent views of the Forth Bridge. Either that or take the Railway path from Coop's car park...