Some questions I have:
Is Summer homeschooled? Does she have local friends or just typically play with her older brothers? Has she gone to a neighbor's house to play in the past? Does the family socialize with neighbors, having joint BBQs, etc.?
When did school end for the kids? Did the boys get a new video game to celebrate the end of the school year? That would definitely distract kids with their focus. (I'm thinking of Summer's poor brothers, who must be devastated.)
Does the family go to a specific church regularly? Has Summer met people there? I believe DW is from Utah. Does that mean the family is LDS? Is there a local LDS church?
Has it been stated whether DW is Summer's bio dad? Did Summer's mom have other bio dads in her life? Did they visit any of their kids if so?
Who was the man at their house during the Oct 2020 incident?
Does Summer have a separate bedroom from her brothers? Is it possible that a peeping Tom could have watched her at night?
I have to say that I felt a bit uncomfortable when DW had the one son stand right with him while he was interviewed on tv. I wouldn't have done that, but of course I don't know the family dynamics and maybe the kid wanted to be there with his Dad so he could feel involved in helping find his sister.