What is the tragic flaw in the characters Amanda, Laura and Tom?
By "tragic flow" I take it that you mean tragic flaw. So, as to the tragic flaw in each of the three characters in "The Glass Menagerie:" there is none. Tennessee Williams' play about a poor family during the great deression is an excellent American drama, but, poignant and unhappy as it may be, it is not a tragic.
None of the characters is tragic:
Tom is stuck in a situation he will eventually worm his way out of. He supports his mother and sister, but he'll soon escape to join the Merchant Marine where he will seek romance and adventure.
Laura lives in a world of her own that amonts to little glass animals and scratchy phonograph records. She is completely unable to take care of herself in any practical way, but her life of illusion is enough to keep her moderately happy.
Amanda, the mother, lives with the fear that Tom will leave and that she will die and Laura will be alone and unable to survive. She copes with this fear by escaping into her memories of the past and by hoping against hope that some gentleman caller will sweep Laura away. This does not happen, however, and never will, and the play ends quite sadly.
It's all very pathetic, poetic, and poignant, but the play is not a tragedy.