When you say newbies, are you talking new to solo's/ tandems , new to paddling Isle Royale, or some combination of?
I would feel very uneasy as well IF this is anyones first solo experience, never mind a 14 year old.
I could see 2 solo's and 1 tandem being more realistic. The newbies could alternate in a solo, and the tandem would be a better platform for a water rescue in the event someone went over.
I think it would take a very experienced solo paddler to rescue someone in the frigid waters of Superior. The shock and numbness of hitting that frigid water unless/even if your in a wet suit, would send most people in to a panic.
Now imagine trying to get someone into a solo without capsizing yourself. In a few minutes they will be at the point they can't help themselves. At least with a tandem, one person might be able to grab hold and the other paddle for shore. In a solo, unless they can hang on themselves, your in real trouble awful fast.
Superior is no place for your first solo experience. I would seriously discuss this and if they couldn't see the dangers, and be willing to compromise for safety, I would bow out or make it a solo trip.
I'd rather have them mad at me, than be witness/accomplice to a accident waiting to happen.
I've swam in Superior all 4x I backpacked the there. By swim, I mean I took a running start, dove in and maybe got out to chest deep water before scurrying back in. In those few seconds, I was already getting numb. Someone goes over in a solo, others try to help, with any sense of what could happen, you can see how it could quickly become a tragedy.
Others might say I'm being a chicken little, but experience has taught me that in situations that have the very real potential to be life threatening, being on the side of prudence and caution beats the alternative.
Now if they want to hump the canoes, and just do the interior lakes, that would be a different matter.
I don't envy your dilemma. But sometimes you have to go against others wishes when you know their doing something that's not in their best interests.
There's a old saying about why you should always wear a PFD while on Superiors waters :question
That's so they can identify the bodies