Mods, mods, mods!
Isn't it fantastic that we can now incorporate mods into our MinecraftEDU experience?
1 - ForgeEssentials includes an authentication module which asks players to set a password when they first log into the world. On subsequent log ins they wont be able to move or do anything unless they input their password.
2 - If you're talking aabout actually making passwords to access doors and chests because it would be cool to have passwords then CompuiterCraft is probably your best bet. You can program a basic security terminal that will allow acccess to doors etc using a specified pin number. If you're just talking about protecting houses and the contents of chests I can recommend MyTown enough its a brilliant mod which allows you to claim a chunk and set who has access to it. In it's most basic form, users type in 1 command (/town new TownName) and they have protected a 16x16 square area of land in which they are the only people who can build and access chests etc.
3 - What do you want to do with teams? CustomNPCs includes a Factions element for players and NPCs meaning if you align yourself with a certain faction then NPCs of opposing factions will be hostile to you. I just read this morning about the scoreboard feature of minecraft which allows you to set teams based on colours (i think) eg red team, blue team etc. This team colour can be used to represent the player name and you can even set things like friendly fire, meaning in a pvp match players from the same team wont be able to hit each other.
All of these mods work with MinecraftEDU with the possible exception of ForgeEssentials as I only performed minimal testing on it for another purpose.
Hope this helps!
Craig