Hi, mcdanielo,
Yikes! That's a lot to see in two days/three nights! You'd be heading north to get to the castles, then it's a long way west to Skye. Balmoral to Portree would be a minimum of five hours, stopping only for bathroom breaks. It all depends on how much time you want to spend on Skye. Are you looking at two days to get to Skye, and two full days on Skye? If you're leaving Edinburgh on the 19th., that doesn't put you back in Edinburgh until late in the day on the 23rd.
Instead of heading for Kincardineshire and Aberdeenshire, if you want to see castles, you should take a more direct route to Skye, and visit Stirling and Doune Castles on the way. Save Glamis/Dunnotar/Craigievar/Balmoral for another trip. However, if you really want to see the East Coast castles, you should visit Dunnottar and Craigievar, and head up toward Inverness from Craigievar.
Skye is a good six hours from Edinburgh, depending on your route. If you visit Stirling and/or Doune, you can pick up the A82 at Crainlarich, and follow it to Fort William. If you want to see the Jacobite crossing the Glenfinnan Viaduct, it goes over at approximately 10:45 a.m. and 3:15 p.m. You'd need to check for the exact time. Make sure to give yourselves enough time to park and hike to the viaduct. If you leave Edinburgh early enough, you may be able to visit one castle, then take the A830 out of Fort William toward Mallaig, in order to get to Glenfinnan for the afternoon crossing. You could then take the ferry from Mallaig to Armadale, to avoid backtracking to Fort William. Also, you may want to check ahead of time to find out if the train is being pulled by the steam locomotive or a diesel. Seeing the train crossing the viaduct being pulled by a diesel doesn't have the same mystique as when it's being pulled by the steam locomotive.
Conversely, you could visit Glenfinnan on your return from Skye. You could follow the A82 to Invergarry, the A87 to the Skye Bridge, and return via the ferry. Be sure to check the ferry schedule, and make a reservation if you decide to go that way. If you take an early ferry on day three, you could catch the Jacobite on its westward journey in the morning, and be back in Edinburgh by late afternoon.
You can do this, but you need to establish your priorities. If Skye is your ultimate goal, you need to give yourselves at least one full day. It looks as though you are allowing yourselves two full days on Skye. So the first day would involve getting there, staying overnight on day one, then spending the next two nights there. There is a lot to see on Skye, and it is impossible to travel fast on the roads there. Make a list of the places that you want to see on Skye, how much time you think that you'll actually have, then get back to us on the forum, and we can let you know if it's doable.
Best of luck with your plans!
Mike (Auchterless)
p.s.: Hope things are getting better for you!