We see the same members of Senta's family in this book that we saw in Brechalon, but their situation changes when Granny dies and Bertice gets married, taking some of the other children with her-- but not Senta, who gets left with a neighbor lady.
The idea for this came from stories from my own family. My great grandfather was the youngest of a very large family, and was still quite young when his parents died. There were several older siblings, who took in the younger ones, except for my great grandfather, who ended up being raised by neighbors. This had to have had quite an effect on a person's psyche. In the book, Senta shrugs it off fairly easily-- probably not realistic, I guess.
As I mentioned before, several of the kids show up later in the series, but not until they and Senta are pretty grown up.