I plan on talking to my son when my wife is not around and tell him not to allow himself to be spoon fed everything that he hears and is taught. It is difficult because he is my stepson and my wife has legal authority in virtually all of the decisions that involve him. I am going to try to encourage him to do his own research and to arrive at his own conclusions.
This is a great plan, in my opinion. Telling him "evolution did it" vs his mother saying "god did it" isn't going to seem like either of you are any different, so he'll just stick to what he's decided. Telling him "don't trust anyone" vs her implicitly telling him "take my word for it" will be quite a contrast and might be enough to make him question why you have the confidence that he should figure it out on his own, while she (and the cult) insist you simply trust them.
On the topic of the earth's apparent perfection for suitability for life, the creationist argument can be defeated without even appealing to natural disasters. If life requires a fairly narrow set of conditions to exist (this can be argued for the life we see here, but might not be the case for all forms of life) then it would make sense that any life that formed would do so in a place that is apparently perfect for it. Furthermore, specialization over 4 billion years would be expected to result in life that appears to be perfectly suited to its environment. It's not that the earth is perfect for life, it's that life has become more or less perfect for the earth.