This sounds more like one of the sects that may be "inspired" by a particular mainstream faith, one of the examples that we see more of in the US media would be some of the Mormon-"inspired" polygamist sects. Of course the actual Mormon church prohibits polygamy, and depending on which sect, you can find all kinds of things that would be contrary to the actual church doctrines.
So it is no surprise that the 7th Day Adventists, or the Methodists or the Zoroastrians will also have their share of "inspired" sects, which are neither sanctioned by nor faithful to the teachings of the actual religion that inspired the sect!
I believe that in your friend's case, the best thing might be for her to talk with the Family Services office in the community where the minor children are living, and it might also be a good idea for her to talk to some local religious leaders there, 7th Day Adventist and otherwise.
While the Adventists, for instance, will of course not be in a position of endorsing or including the spin-off sect in any way, they might have information about them, and advice for your friend. There could be other people there who have been in your friend's shoes, and if they managed to get them unzipped, their stories might also be able to help her work toward a solution.