Keep in mind that Sakya is mostly just porting this emulator (excellent user interface, by the way!) and I don't know if PCSX-ReArmed has any multiplayer support built-in at all.
PCSX-Reloaded does, but ReArmed is totally different.

Ask Notaz in this thread whether the OpenPandora version supports multiplayer and it's just a flaw in the Maemo port, or if the current codebase simply doesn't allow for player 2 input.