Hi Martin,
Hmm, how to say this politely... your wife is most likely going to be who the dog bonds with the most, so she should have the most say in the matter. She'll be home + she's the adult. Realistically, she's also who is going to be doing all of the hard work raising it.
Your 12 year old, unless he takes over all of the training, cleaning, & feeding without argument, is not who the dog will naturally look to for guidance. He's young and has probably lots of interests. A puppy is fun to play with, but is he really willing to voluntarily do the work too? Dogs do realize that children are human puppies and they don't naturally mind them. He's also going to be away at school for a good chunk of the time. 6-8 hours is eternity in a puppy's day. You'll be away every day too.
That leaves good ole mum for entertaining, correcting, housetraining, feeding, and cleaning up after puppy. I hope she's ready for all this.
good luck with your search
toodles