let me try and tackle your question sir,    weapons in demon's soul can be use by which ever class there is no restriction to equip it and start using it, BUT which class u choose will determine what stats u start with.    weapons will rely on stats that u hv , sometimes u can equip a weapon but u hv negative stat when u wield that weapon.  so u wouldn't want that.  as for attack pattern , i never play MH in my life , but yeah attack pattern do varies for each weapons.  btw a 1h weapon can be use as a 2h weapon , so ur thief can wield a dagger/sword/whatever using 2h.  just press triangle for 2h the weapon.  

i hope my explanation is correct.

LOL! a "smart" way to play