"Hide from Undead ends like invisibility d- excuse me. Hide from Undead ends if any of the hidden individuals channel positive energy or attacks anyone or touches any of the undead. Also they get a save, so it won't always work. The Greater version allows a save but it'll be harder because it's a higher circle spell, and instead of it automatically ending if someone attacks or channels or touches an undead, they just get another save then. In both cases if they guess you're there they can act like they've guessed you're there, just not in a way where they can sense you. Speak with Dead only works on corpses, not undead, and gets - probably ten questions or so if I cast it, maybe more, and how useful the results are is never fantastic and will depend on whether the dead creature would have been cooperative with me in life, and it has to be mostly intact to be able to talk. I'm not actually sure if the soul in the afterlife can register the conversation or not. It will only answer questions it could have answered before dying, so probably not but it could just be another limit on the spell."