I'm looking to build an Omindin/Auradin. I've been looking online for a few hours and cannot find an answer to this question.

Using an Act 2 NM merc with Holy Freeze aura, and using Dragon armor, and Dream helm, do the auras apply damage/effects simultaneously, or do they cycle their effects/damage?

Also how would Dream apply its damage in conjunction with my Pally wearing 2x Dream? I believe because it is a separate source, the 2 Holy Shock auras work together separately. So 1 level 30 aura, and 1 level 15 aura. Is this correct?

Try post your question in the right section This is the Ladder Slasher section, you should try the Diablo II section.
Have you tried look in the Strategy & Guides section btw for auradin guides? Worth taking a look here:
https://forums.d2jsp.org/forum.php?f=87

Sorry I'm new to this stuff. Thanks for the info.