I think odds of decent weather are better than 60/40. Storms in October are few and far between, so if you watch the forecast, you should be ok in that department.
As for the newbies, if you keep taking different people, it is just a matter of time before you take someone who is adversely affected by the altitude. It is like rolling the dice -- one of these times it will happen. Just be sure, like you did with your son, that they snack regularly and stay hydrated so those factors don't get in the way.
And I hope you have both good weather AND altitude-resistant hikers.