Quite a few people could have been aware of Summer and the property. The abductor could have easily been invited into the home at some point.
I'm also following the case of
Maëlys de Araujo. She was abducted from a wedding reception, raped, and murdered by a friend of the groom. (Some friend!) Her killer was identified only because there were quite a few video cameras in the immediate area.
I think that one of the sex offenders who lived near the Wells family is the perp.
I'm not sure whether you're in the minority in believing that the parents were not involved. A very vocal clique has been going after the parents, but I have been convinced from early on that it was a non-family abduction. I was able to rule out DW (the father) very early in my own mind; CBW (the mother) can't be ruled out quite as easily because she was at the home, but I don't think that she was involved. I don't know how reliable her assessment of the timeline is, though. Her estimate of leaving Summer unsupervised for two to five minutes may be low.