This story reminded me of THE GUNCLE. Lillian’s old friend Madison asks her to look after her two stepchildren who have this problem of spontaneously combusting. Their unsightliness upon the family (Madison’s husband, their biological father, is a Tennessean politician) relegates them to living outside the family home. Lillian bonds with Roland and Bessie as well as fellow employee Carl. Lillian is a spunky protagonist with her own family wounds. 

I think this is a great one to pick up if you’re going to be a stepparent. While it does have some magical realism (spontaneous combusting), the vast majority of this novel is very grounded.