^The backround story looks good to me. However, you should keep in mind the implications of Diver's actions. If Diver can hear what Tooele said, even though Tooele took extra precautions not to be heard, then Ruddy and Edmont will hear what Diver said, and Ruddy will have his suspicions confirmed.
This is likely to upset both Ruddy and Edmont, but Ruddy even more so. Since he tends to take things too far when he is convinced of the correctness of his ideas, he could go and confront his mother. The problem with what Ruddy is doing is that what he knows by this point is by no means the whole truth.
Ruddy, Edmont, Tooele and Lamby may be attentative and even quite smart, but they are children and still cannot possibly understand the true intentions of their mother, and their interpretations of her actions are fairly superficial.
Though I do not know what David has exactly in mind, I'm pretty sure it's not true that Ms. Swimmer wants to go to permanently live with another herd, or that she would risk her children's lives for something you can live without. She is far more experienced than her children and has given the issue way more thought than they could. There is a lush place out there in the winter than can be provide more than enough food for all swimmers. It is quite possible that this is the same place where Ms. Swimmer and her husband came from, since the Mysterious Beyond has been greening from greater rainfall in the last few years, andthat news have arrived jsut recently. Ms. Swimmer has talked with other swimmers and has likely made detailed plans on who will travel, which way they will they travel, and how they will come back, and likely has a fallback plan or two should things go wrong at some point.
When Ruddy confronts her with what he knows, she is likely to be offended and angry. From her perspective Ruddy's sketch of the situation would appear cartoonish and possibly even malevolent, if Ruddy could really think such bad things about his mother (he doesn't really, but he's not acting completely sane at this point).
So, unless some more level-headed sibling stops Ruddy (Edmont could do it, but he would be angry at his mother too at this point), Ruddy will likely hurt his mother's feelings and complicate the trip for everyone.
