Pidgin – How to Fix Offline Buddies Issue

As already pointed out, Do Not Disturb does not turn off notifications. If you want to do that, go to Tools > Plug-ins (or Ctrl+U keypress) and uncheck the 'Libnotify Popups' plugin that is responsible for the notifications. Enable the plugin when you want to re-enable notifications again.

You can also choose to configure the conditions on which the plugin provides popup notifications. One of the conditions is "Only when available". Check if selecting this will stop notifications when you set your state to anything other than Available.

As far as I know, you can create separate groups for each account (for example: "AIM 1" and "AIM 2") and then move your buddies to the right group. I don't use AIM but this works perfectly for me without any plug-in with Pidgin 2.6.4 using MSN. (I have a "work" group for my first and another for my second MSN account.)

Or alternatively you can run separate instances of Pidgin with sudo -u otherusername pidgin (or gksudo -u otherusername pidgin). Note, that you have to create a second user to do that, have the proper rights to run sudo and enter your password every time you run Pidgin like that, which can be a little annoying too.