Talk to your exams officers. If you are doing this because that's how your college offers the courses then they should take care of it. If you are doing it 'privately' then you could be stuffed as it's not their problem or made to pay for the supervision you'll require between the colleges.
+ the June sittings for 2 exams I took in Jan are that day: GGA4 geog and 2887 economics (the hardest one lol)..so if I had to resit them both eeeeekkk!! it would be 4 1.5 hour exams = 6 hours on one day which is the limit I believe? Lets hope I don't have to resit (at least not both lol!).