I suspect they are “garden variety” denomination because any living around me that I would call “sectarian”, surprisingly, send kids to local schools and live in a more community-type way. JMO.
How extreme was the family itself I don’t know.
About Fall City. It is closer to Sammamish. Sammamish is well-known and settled with mostly IT-workers. I suspect that when the cost of Sammamish houses became insurmountable, people started settling close by, in Fall City. They do have a High School, per district, and a good one. Because the said IT workers would try to make it very good. So homeschooling was strictly the parents’ choice, IMO. The problem, if you look at the map, is public transportation. With five kids of a different age living at the lake, I think mom would feel spread too thin either way (not judging, thinking of how it was for her). The only thing I know about Fall City, and specifically about it, before this tragedy hit, is that kids need own cars to drive out. It is a true “bedroom” community. So either someone has to drive you to your friends nearby, or you have to stay in your house. Everyone probably felt isolated; we don’t know how it affected mom herself, alone and with five kids of a different age.
I think COVID might have split people even more, but just my suspicion.