Presumably Jeep and Alfa will share what was the Kia half of the showroom, I dont think AC or indeed the majority of people see Alfa as a "prestige" brand, with only the Mito and Giulietta on sale for so long, I worked for Arnold Clark when they took over Reg Vardy/Evans Halshaw Fiat/Alfa in Paisley at the time AC lost the Alfa sales franchise and it was hard to see Alfa as a prestige brand sharing a dealership with cheap crap Fiat rubbish, even although they had the 159, Brera and GT at that time. The Fiat link sorta cheapened them, and I suspect thats why Alfa mainly got independent dealers like Western to sell them standalone or away from Fiat.
As for locations, I dont think theres a lot of ready made premises that Jeep/Alfa couldve gone into in Aberdeen, in order to move Kia they had to move Ford commercials as an add on to the Girdleness Road Service Centre, so that Kia could have their premises. The talk for a few years was of a FCA group dealership in Aberdeen although originally the talk was it could be at Kemnay, which has since closed.
Arnold did have a smart showroom in the area you mention which they ran as a Lexus dealership, but since losing/dropping Lexus they sold off the premises, and the only other spare dealership is the former Mazda one at Canal Road Mounthooly which is being used as a Hire Drive/Rental depot for AC, im nowhere near Aberdeen so not sure if thats a good location for a car dealership.
People say Perth AC Kia/Jeep isnt going to become an Alfa dealer, but to my knowledge Jeep will not be run as a separate franchise like it used to be before Fiat took them over, the plan was dual joint Alfa/Jeep dealerships, or at the very least Jeep in with Fiat/Abarth, but it doesnt look like Jeep is moving to the new Fiat showroom Arnold Clark are building and relocating to in Perth. 3 dealerships is simply not enough, particularly when 2 are Arnie Shark and grouped with other franchises like Fiat and Vauxhall where the salesmen will be more interested in pushing sales of Corsas, Astras, Puntos, 500s etc.