@Arrellcat
There is a particularly nasty chicane required on the old A90 (between Agilent and Dalmeny) just as the path crosses the railway. There is a garted barrier and cyclists have to mount a curb, shoogle through a narrow gap, all on rough ground and tricky enough for this cyclist without any trailer.
If this trailer is as big as people say, you may get stuck there.
You can probably follow the A90 Path via Viewforth to join the Loan (there are a couple of barriers, but hopefully passable), but I'd go via Burgess Road and Station Road to get to Dalmeny...
To be totally certain, I'd consider taking the on-road route Ferrymuir Gait - Ferrymuir Road - A907 - Burgess Road - Station Road - Bankhead road to get to Dalmeny Village.
Also, the signage on the north side of the bridge bridge that @bax refers to is unpleasant enough for bikes only, particularly with accelerating traffic coming behind you.