Here's the Reading Order For V.C. Andrews "Dollanganger" Series

(1). Flowers In The Attic
(2). Petals On The Wind
(3). If There Be Thorns
(4). Seeds Of Yesterday
(5). Garden Of Shadows
(Note: Garden of Shadows Is a Prequel To The First Book "Flowers In The Attic",
But it was actually written 5th in the Series. You could read it first, but it isn't necessary to
to do so in order to understand the storyline.)