Should we boost Str to 10-11, since they didn't have a damage penalty and rely on constriction? A Medium constrictor snake has Str 17, Dex 17, Con 13, by comparison.
Give 'em the usual snake racial skill modifiers?
Skills: Snakes have a +4 racial bonus on Hide, Listen, and Spot checks and a +8 racial bonus on Balance and Climb checks. A snake can always choose to take 10 on a Climb check, even if rushed or threatened. Snakes use either their Strength modifier or Dexterity modifier for Climb checks, whichever is higher. A snake has a +8 racial bonus on any Swim check to perform some special action or avoid a hazard. It can always choose to take 10 on a Swim check, even if distracted or endangered. It can use the run action while swimming, provided it swims in a straight line.
Thinking about the fact that the Opawang doesn't control them, should they be immune to commanding? That's not quite the same as mind-affecting, I think.
Edit: I'm also fine with the snake skill modifiers.
The "immune to commanding" bit would be a bit odd. I proposed in the Opawang that we change his ability to a Su compulsion effect, which would allow us to change these guys to simply "immune to compulsions". Does that work?
Spectral Scales (Su): An island serpent's ghostly scales make it difficult to target an island serpent. Any melee or ranged attack directed at it has a 20% miss chance.