Can I use multiplayer with only one login on 2 different computers

Question

I have purchased Minecraft for my 2 sons and they have loved playing it for the last few months.  They both play at the same time on 2 separate PCs, using the same login.   The other day I set up a minecraft server on 1 PC so that they could play multiplayer, just the 2 of them, on our home network.  I could access the same shared world on either PC using the 1 login username.  However, it didn't seem to be possible for them both to play at the same time - I got error message "Connection lost   Failed to login: Bad login".  I am guessing this is because it is not possible to play multiplayer with a single login username?  To try and get round this, I set up a second username for my second son, but not wanting to pay a second time for Minecraft, I got him demo access only - so of course he can't have access to the multiplayer version.

So....how can I have my 2 sons play multiplayer together on our home network without buying Minecraft a second time? (I mean, bringing up kids is expensive enough without having to buy the same game twice for the same household)

Answer 1

Hello Callum,

I've read on the internet how you would be able to do this. It requires some knowledge about CB servers though:
 

Turn your server into a bukkit server and get the plugin xAuth. Disable the built-in authentication of this plugin and then it should allow for cracked clients.
 

Get bukkit here: http://dl.bukkit.org/downloads/craftbukkit/

Get xAuth here:  http://dev.bukkit.org/server-mods/xauth/
 

Good luck.

Answer 2

if they are playin multiplayer they have to be playing on different servers or when they are playin single they can play together but their minecrft skin needs too be changed different ffrom one of each other