This source gives lots of information but to add to this discussion of the Sisters of Maria I here is this: I have put ? or undecided if the information differed...
All of the talents of the Braganza family was said to be entrusted in Donna Maria Anna, second of Joseph's Daughters. Shorter and thicker in her Person than the Princess of Brazil She was more agreeable in her countenance possessing a ruddy complexion as well as a more animated expression of features. Her mind was likewise expanded and her understanding cultivated by polite knowledge. Many of her hours were dedicated to reading and she was regarded as superior to bigotry. In addition to these solid endowments she joined great taste and skill in music with a fine voice. though the most accomplished of the three Sisters she was nevertheless doomed to remain unmarried at their Father's Court having attained in 1762 her thirty-sixth year.
Nature had in some respects been more bountiful to the third ? Princess Donna Maria Benedicta who was likewise considerable younger being only six and twenty years old at this time. Though low in stature, clumsy and much inclined to embonpoint her face was very handsome; her eyes dark and eloquent, her complexion fair, the contour of her countenance rather round that oval, and her features small as well as delicate. but she was not considered to possess the superiority of mind that distinguished Maria Anna. About seven years before the time of which I speak a treaty of marriage had been set upon between this Princess and Emperor Joseph II who was then recently become a Widower by the death of his first wife, a daughter of Don Phillip, Duke of Parma. The negotiations proceeded so far that preparations were made for transporting her from Lisbon to Flanders in her way to Vienna: and a ship constructed expressly for the purpose in the Brazalia magnificently decorated lay waiting in the Tagus. (unsure of word) But the intrigues and exertions of the old Dowager queen of Spain, Mother of Charles III, and Grandmother of the Princess herself, who was incensed at the endeavors of the Marquise de Pombel, to assume the exclusive merit of this alliance rendered the plan abortive.
Wraxall's Historical Memoirs
http://books.google.com/books?id=Cq8RAAAAYAAJ&pg=PA82&dq=Joseph+I+of+Portugal+and+his+daughters&lr=&ei=w77oR-faNozcygTM9tDfCQ#PPA83,M1