Alfonso
Technically, neither Nairn nor Cruden Bay are in the Scottish Highlands, so if your group is full of geological purists you'll have to stick to in and around Dornoch.
However, even if you include the NE coastal plains, Dornoch is clearly the finest course in the area, and the only one truly vaut le voyage, in Michelin-speak. I think you have two alternatives.
1. Sticking to Dornoch as a base (or maybe Tain, given the size of your party and the dire hotel situation in Dornoch mentioned by David T) and playing the Championship course there as often as possible, with occasional forays to (in order of my preference) Brora, Golspie and Tain. Relax, chill out, and really get to know one of the truly great courses in the world.
2. Spend two days in Dornoch playing 3 rounds on the Championship course and one at Brora, which is truly vaut le detour. Then move southeast to Aberdeen (stopping at Nairn on the way if you wish, although I do not think it is quite worth the detour). In Aberdeen, stay in one of the decent country house hotels near the city and play Royal Aberdeen, Murcar and Cruden Bay. In my opinion each of these courses is of roughly equal quality and better than either Brora or Nairn. If you have some free time while you're there take ramble over Balmenie links to see what The Donald is planning.
Regardless, enjoy!
Rich