Question: What order do the flowers in the attic books go?
Disambiguated questions and answers: question: What order do the flowers in the attic books go including the spin-offs?
What order do the flowers in the attic books from the Dollanganger saga go, not including the spin-offs?
answer: Flowers in the Attic, Petals on the Wind, If There Be Thorns, Seeds of Yesterday, Garden of Shadows, Christopher's Diary: Secrets of Foxworth, Christopher's Diary: Echoes of Dollanganger and Christopher's Diary: Secret Brother
Flowers in the Attic, Petals on the Wind, If There Be Thorns, Seeds of Yesterday, and Garden of Shadows
Natural Questions answer: If There Be Thorns
Petals on the Wind
Garden of Shadows (from the Wikipedia article "Flowers in the Attic")