for travel to Orkney: https://www.orkneyferries.co.uk
No, they are the inter island Orkney ferries, the other company from the mainland (at Gills Bay) is Pentland Ferries- https://pentlandferries.co.uk/
Gills Bay is pretty much equidistant between Thurso and Wick.
But Northlink are the better company to Orkney because both Scottish Citylink and Ember bus run direct to Scrabster Terminal from Inverness, rather than having to get from Thurso Rail Station to Scrabster,
The Citylink service is really run by Stagecoach North Scotland so the buses are not usually Citylink liveried- they are either Stagecoach yellow distance or Megabus livery.
Stagecoach won't get you to any mainland Skye ferry terminal- that is Shiel Buses from Fort William to Mallaig, or Scottish Citylink for services over the Skye Bridge (and soon Ember Bus as well).
Stagecoach just run services on Skye so to the three ferry terminals on Skye.