Well, to be fair on the DR, we've done stuff like obsidian before, haven't we?
The rest is looking good.
It may have been Maztica (or was that only for weapons?).
Anyway, I guess I'd go with cold iron for the DR, since I wouldn't mind playing up the connection to demons a bit.
Let's toss 'em both into the mix.
Since these things are oracles, shall we give 'em this?
Knowledgeable (Ex): A being of the ball makes Knowledge checks for any Knowledge skills as if it had a minimum of 10 ranks in that skill. To surpass the 10-rank minimum, the being must assign more than 10 ranks to the skill as normal.
Sounds good. I wonder if they shouldn't have augury and/or contact other plane as SLAs as well?
Skills: 12 at 13 ranks
Bluff, Concentration, Gather Information, Knowledge (the planes)...
Feats: Multiattack, 3 more
Blind-Fight, Eyes In The Back Of Your Head, Jack of All Trades...