I always LOVED Trixie Belden as a kid….and spent my own money to buy as many as I could!
How about The Saturdays? That’s a two brothers, two sisters story.
The Switherby Pilgrims and Jamberoo Road are about a sibling group that is made up of “orphans” (some technically orphans, some practically orphans). And throughout the books, some of the children make bad decisions, live the consequences, and go on to make themselves better. One sibling makes a life changing decision for the betterment of the family. There are lots of good examples in those books. We read them when we studied history (they are about English children moving to the Australian Bush back in the 1800s). Plenty of adventure to keep everyone interested in the story, too.