I think you should be able to fix this using TextAloud Pronunciation Dictionary Maintenance. From the TextAloud main window, click Tools -> Pronunciation Dictionary Maintenance, and add a dictionary entry like this:
Set the Text Matching dropdown to "Simple Text". In the Simple Text field, use "Mr." (without the quotes). Then set the Pronounce Using dropdown to "Respell", and respell Mr. as "Mister" (without the quotes). The Word Boundary dropdown should be set to "Word Boundary Required".
Then add a similar pronunciation dictionary entry that respells "Mrs." as "Misses".
Let me know if that doesn't help.