Of course it's about the wrong-doer, Chrismas. Because the wrong-doer has to learn why it's wrong, and not to do it again. In the case of the 'consent' issue, children don't reach some magical age where they suddenly realise that they shouldn't do things to one another without permission. A 12 yo boy drawing on his friends with Sharpie needs to learn now that what might seem to be harmless fun can be interpreted otherwise by the recipient. However, a massive punishment for this particular misdemeanour would just make a 12 yo feel that his parents are mean and unfair and that he is the victim. I'd have thought the education aspect was more important than the punishment aspect (and I don't see what confiscation of electronics would achieve, other than making the 12 yo feel aggrieved. It isn't his place to feel aggrieved: it's his place to feel sorry and a bit ashamed/sheepish).
In this particular case, I would have firstly asked mine why they thought it was a good idea to draw on someone with permanent marker. Did they think it would come off? Did they think at all? How did they imagine their friends would feel about going to school/clubs with marker pen on their faces? How would they feel if it were them?
I would have (re)explained to mine why 'harmless fun' isn't harmless fun unless all parties agree to it. I'd also reiterate that it isn't ok to do things to people without their permission. This applies to interfering with them physically, or taking/posting photos of them.
In terms of reparation: once I thought they had even the vaguest idea of why their behaviour was wrong, I would firstly ask them how they thought they could make it better.
(I have found that it is often a good idea to get children to come up with ideas, as they then 'own' them, rather than just being told to 'say sorry').
If they really couldn't think of anything, I'd suggest they firstly apologise to the other boys. This can have a remarkable effect on children, who are far more forgiving of one another than adults can be of them.
If I thought it really necessary (and I'm not sure that it is, in this case), I might suggest they approach the other boys' parents (if they have the opportunity - I realise the DC in the OP aren't at the same schools) and explain directly why they did what they did (even if the explanation is "we just thought it was funny"). I would then expect them to apologise for having behaved in that way. I would warn the DC that the other parents might give them short shrift - though I think most parents would actually be pretty appreciative of children having the courage to own up and apologise. In fact, a lesson that adults need to teach children is that if you do something rubbish, recognise it, and apologise, you are forgiven and everyone moves on. Though some adults aren't much better than 12 yr olds themselves.
If the children can't do it in person, I'd suggest they write a short note along the same lines.
Sorry - a bit long. But you did ask!