Welcome to the joys of travelling from ABZ, I've not had a flight this year that hasn't been disrupted. There's been such long queues to check in too (Sometimes only one check in agent sometimes two, on the odd occasion they have opened check in 2 hours before the flight leave, the worst was 90 minutes before the flight departed.) I've given up travelling from ABZ and just get the train to/from EDI. Which is a shame as ABZ isn't that bad an airport, there's never really big queues at security, the food is better in the (paid) Northern Lights lounge than the BA lounge.
Tram and Train from EDI - ABZ is really easy. Exit the terminal, get on the tram, about 25 minutes later get off at Haymarket, down a flight of stairs and get on a express (!) train to ABZ. The LNER trains are better than the ScotRail in my experience.
For the return on Sunday you could take the train back to EDI or do EasyJet from ABZ to LGW
The sleeper would be a good idea, but looks sold out on the Friday night and there is no service on a Saturday night