I read an early on report last week that I can't find again, but the way they had written it was that the oldest daughter was removed from the home when Wesley posted bond and was expected to return home.
I think that is a major reason why people assumed he was living in the house, but it turns out that according to his terms of release he was not staying with Sini.
If CPS thought though that the dad being free was a possible threat to the OS (older sister) that would explain why they took her at that time.
I can't recall when they searched the homes with FBI and dogs, but my GUESS is that the cadaver dogs made a hit, likely both in the house and on the cars, and that is the reason the OS was removed.