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That parents would find a hobby that means they don't intrude in, interfere with, or otherwise hinder their adult child's life by dropping by the house incessantly, or criticizing the LW's spouse/children/house/pets/looks.
Even more, I am shocked that anyone would get so thoroughly unglued by their parents' finding an outlet for their time and intellect. Whatever the hobby, genealogy...church activities...the local Big Ten football team...prize winning roses...Westminster dog show...X-Box...it seems clear that the LW is going to be jealous of the parents having a life beyond focus on LW.
Let them be. They will be fine. And so will LW when s/he realizes that, after they're gone, the parents' quirksome nature on the genealogy bit will only make for more interesting stories to pass along about them...when LW gets interested in the genealogy bit when s/he reaches the hideously old age of 60.