Hi! Do your friends want to go direct, or do they not mind a connection somewhere?
I know that companies like Thomsons (and I think Thomas Cook) fly from Aberdeen on certain days of the week during the "Summer" season, typically April to October. These charter airlines go to Sanford International Airport. I have never flown that route so I can't give you any info on it.
If they prefer to go with a scheduled airline there are options from Glasgow and Edinburgh like COntinental - which seems to be a favourite of many - where they connect in Newark and that is year round as far as I know. I have always gone to Manchester and flown from there becasue I could never get flights from Glasgow. Next year I am going Glasgow, but only because I booked 17 months out and was flexible enough on my dates to be willing to pull DD out of a week of school.
It all depends whether they are set on a package or doing it DIY as well. I have always done a package because I wasn't confident enough to put the trip together myself, but I have vowed that after the next trip I will do the DIY thing as it is usually, although not always, more cost effective.
One point on the Manchester flights: the 10.25 am departure gets you to MCO early afternoon which really gives you the best part of the afternoon plus the evening to settle in and go and do something.
How many people are there in your friends' party?