If you mean splitscreen then here is a video how to hack it: http://www.YouTube.com/watch?v=6Yfv_7yEshM
If you dont want to hack, then i'd say just use riot shield it's simple: one guy equips riot shield, the other keeps shooting on it, the guy with riot shield gets xp. You can take turns. If you dont like any of these i'd say just keep killing other people.
10th prestige Level 70 as Online and Offline have the same level and prestige Caps.
No.
If you are in a private offline match, yes, you level up just like you do online and you will unlock the class customization at level 4.
The fourth level in Call of Duty Modern Warfare is No Russian (which can be skipped.)
Level 42
It aint MW3 fault, because ur info is stored online, and not on ur console, when ur offline, u cant get any level ups, because the info is not being transmitted to the master server.
nothing
You unlock it at level 36.
Level 38
You need to level and complete challenges
The Lieutenant Rank is at Level 34
If you're talking about the museum level from Modern Warfare 2, then probably not. That was a one time thing.