Here is what I think/remember.
Mrs. Huber's sister never visit her sister, and were there no pictures of her sister in the house?
I think this is very possible. The sister has in not so many words said that she is sort of glad her sister is dead.
She would have had some family pictures.
Maybe not if you are referring to Mrs. Huber.
Mrs. Huber borrowed her blender after all. They must have spent some time together. You wouldn't borrow, or ask to borrow an appliance from a casual acquaintance would you? Furthermore, didn't Mary Alice mention any of this to her husband?
Didn't Mrs. Huber borrow the blender the very day Mary Alice killed herself? She wouldn't have had time to tell her husband. But the way the show has played out this first season, I wouldn't be surprised that Mary Alice had not told her husband about the blender. Everyone seems to be getting into each other's houses all the time!
Didn't Paul say that Dana was a 24 year old woman who was alive and well?
Paul told his son that Dana was very much alive but I don't remember ever hearing the age. I don't know if Paul referred to Dana as a she either.
Even if Mary Alice knew that Mrs. Huber's sister was an ex-coworker, I don't think that would mean much to Mary Alice if she knew the sister and Mrs. Huber didn't have a good relationship with her. Also, I don't think Paul recognized the sister until he saw the video tape of Mary Alice at work.