I think it boils down to the maturity of the parent. As long as we are teaching them between right and wrong, real and pretend (which as parents we should be doing anyway) then I see nothing wrong with enjoying a GAME as a family.
My girlfriend and I have seperate accounts and play on the same xbox and I got the DLC a week after it dropped and we both had it, however when the game launched and we got the hardened edition, I got the camos and she didn't, we both got the calling cards and I let her have the claw avatar prop.
It's not often you have to have a dlc on two accounts. It'll be useful if you're going to give a friend it for free.
No, the peacekeeper for me was a pain in the azz to gold. It seems to have changed since it was released with the DLC.