The only thing you could do if the other family is not arriving at the same time as you is go to the Guest Relations window before you enter the park and have them check in his ticket early. That will only check in his tickets though and not the other components of his resort stay.
I work at front desk and do it all the time daily. I suppose there could be an option to opt out of getting a magic band but not everyone brings their old ones nor realizes they can use multiple sets so to be safe they haven't given that option yet.
Like I said earlier if guests do not want multiple sets of MagicBands they can tell the front desk cast member so and then the MagicBands are deactivated and they are recycled as well as with the boxes.
You should have a 15 min leeway after your time has passed. Just as with dining reservation. Although it is at the discretion of the cast member working the attraction entrance.
There was system challenges at some point last weekend so it's possible the system was down and they just went by the honor system assuming you were are resort guest and/or annual passholder.
Or you could not customize the new set and when they go to give them at check in tell them you want to use your old ones. They will verify that the old ones are on your current room reservation and deactive and recycle the new ones. Voila!
Are you going to the parks again any time soon? I'd go to Guest Relations. They may be able to figure out something on their ticketing system or call the cast IT line at least and try to figure it out from there.
You can't. As of December 2013, photopass+ is no longer available for purchase. But those who had bought it previous to that are still entitled to that package when they arrive at WDW.