My first thought would be at 3 to 4 days is very limited time to see much of Scotland. I'm not an exponent of must sees, it's all down to people's interests and one person's must-see is another person's snoozefest, however there are maybe 8 or 9 well known locations/areas that come up regularly on here and other similar forums (although there are dozens of other less well-known Scenic spots/points of interest) . With three to four days you only have time to spend meaningful time in maybe a couple of these locations. Scotland looks small on a map, but outside the more populous Central Belt many roads are narrow and twisty and it can take a long time to travel between two places that look close on a map. As a result if you want to cover much ground in such a short time independently it involves a lot of driving and seeing places virtually by driving past them!
I'm not an expert on Ireland but I would suggest that much of what I said above about Scotland applies equally to Ireland. As a result it may be worth reconsidering and focusing your full seven days on one of either Scotland are Ireland on its own. 7 days would allow you to get a good impression of either country - and obviously because this is a Scotland forum I would say you should pick Scotland! Scotland does have more in the way of cities and larger towns, so perhaps this might provide more interest for the younger members of the group.
I don't think you need to worry about boredom. Scotland is far more than just pubs and distilleries - indeed I would suspect most foreign visitors probably don't visit a distillery. We have cities, shopping, museums, art/Modern Art, culture countryside, mountains and Lakes, hiking, cycling, extreme sports and more!
It would be helpful if you could outline what things your party is interested in so as to give better recommendations. However with such a short time the best plan would probably be to stay in either Glasgow or Edinburgh for your 3 or 4 days, look around, do a day trip to the other City by train one day and perhaps on another day take a day trip somewhere like Loch Lomond, Stirling or St Andrews by train. Companies like rabbies and discover Scotland offer day tours on small buses to the Highlands from Glasgow and Edinburgh. These get good reviews but given the distance they are very much whistle-stop tours with a lot of driving/sitting in a bus
Alternatively if you want a countryside focussed itinerary id probably fly to Glasgow, get a car and drive straight to somewhere like Loch Lomond, Oban or Glencoe/Fort William then tour around the Highlands for 3 days. Bear in mind that skye and the far north are a really a bit too far to travel in that time. I guess it epends on your interests and preferences.
Can I also ask where in Turkey youre starting from and how you plan to get from there to Scotland/Ireland, how you're traveling between Scotland and Ireland and how you plan to get to Spain? Availability of fights and routings may influence your choices.