Concerning Mummies....

1. Their Mummy Rot: ability is both a Curse and a Disease. How does this hold up against people immune to disease, like for instance a Paladin?

2. Despair (su): Is this a standard action the mummy uses on his turn, or is this 'always on', meaning the second the encounter starts people start throwing saves?

Thanks for the help!

1. If the target is immune to supernatural diseases along with normal ones, it will not work on that target.

2. I forgot the write-up, you'll have to quote it.

Despair is an aura (see the statblock) therefore it is considered always on.

Despair (Su)

All creatures within a 30-foot radius that see a mummy must make a DC 16 Will save or be paralyzed by fear for 1d4 rounds. Whether or not the save is successful, that creature cannot be affected again by the same mummy's despair ability for 24 hours. This is a paralysis and a mind-affecting fear affect. The save DC is Charisma-based.

And does this means that if combat starts with lets say 4 mummies, all players must roll the save 4x? 1 Each mummy?

On the statblock, under the Aura section at the top, it lists Despair under that. And under Fear Aura, it calls out Mummy's Despair as an example and says it can be activated as a free action.

In addition, the wording of Despair seems to show that yes, if you are in the range of all of the mummies, you would suffer the consequences of all of them.