Dual logging is legal, with two accounts logged in separately. More than two accounts is not. More than two characters on the same account logged in would be problematic in any case. The only way to transfer items and funds between accounts is the normal Trade function. Because PWI spells can be stacked up to two at a time, it makes it easier for two Arcane characters to cast continuously, as long as lag or other obstructions permits, by hitting a spell icon to begin a spell, hitting another to follow, then switching windows, and repeat.