Recoil, considering the load (gunpowder quantity), height of user, whether the blast is anticipated, whether the butt stock is tucked in tight or not... I would start with saying that a 98 lb woman (no offense, but I'm considering upper body strength) who knows what she's doing would still be standing. Anyone larger, not doing anything stupid (i.e. holding the butt of the weapon in the middle of the chest, against the forehead, etc.) would have no problem.
a 12 gauge shotgun can shoot about 30 yards accuracy
You could eaither shoot dove with a 20 gauge shotgun or a 12 gauge shotgun. You should also use a bird shot shells
No, you can not shoot anything but 12 gauge shotgun shells through a 12 gauge shotgun. Never use any ammunition other than what the firearm was designed for.
Depends on your parents
A 12 gauge shotgun cannot fire 20 gauge shells.
Yes, if it is a 10 gauge shotgun.
Yes
, It depends on the 12 year old. Can he shoot a 20 gauge shotgun? If so, then he should be OK with light ball in the Mosin-Nagant. If you reload, you might work up a load with Trail Boss to give him less kick while his shoulder gets conditioned. Josh Smith smith-sights.com
You will have to shoot all of them through your shotgun to see which one(s) it prefers.
no
A shotgun is really the only one to use so a shotgun 12 20 gauge maybe 410. if you hit it in the right spot
Ensure you look at the stamped shell gauge on the side of the receiver (12 or 20 Gauge). Should be able to take 2 3/4" and 3" shells.