Confused by the end of Masterpiece's "Little Dorrit?"

This is what I understand:

Mrs. Clennam is not Arthur Clennam's real mother.

Arthur's real mother was a theatrical dancer who lived in Frederick Dorrit's boarding house in time's past.

Frederick was the dancer's (Arthur's biological mother) guardian and had no children of his own.

Frederick is the kindly brother of Edward Dorrit whose youngest child is Amy. 

Arthur's father (Gllbert Clennam who died at the beginning of the story), "being a weak man" had an affair with the dancer. The child of their affair, Arthur, was taken by Mrs. Clennam from the dancer to be raised as her own son in exchange for ongoing support and a promise to never to see her husband again.

Before dying of a broken heart from the loss of her child, the dancer wrote to Mr. Clennam's uncle who had raised Arthur's father (Gilbert), telling him of the sad tale of betrayal. Wanting to help, the uncle rewrote his will to benefit a young girl, who, poor as the dancer, was born motherless on the same day the dancer died. Her name was Amy Dorrit.

Mrs. Clennam, in fear of the truth being known, did not fulfill the wishes of the will and withheld the money that would have benefited Amy and freed her from a life of poverty in the Marshalsea prison.

When finding out the truth, Amy selflessly forgives Mrs. Clennam.

Amy and Arthur are not related by blood but by stories of unrequainted love that occurred in Amy's uncle (Frederick Dorrit's) boarding house.

Still confused?