Marge is a practical woman, mother and wife.  She has grown stern over the years, dealing with her husband's paranoid fantasies, but deep down she still loves him.  In contrast to her husband, she is flat and even-tempered - skeptical, pragmatic, bored.

It'd be very cool to also have someone who could voice the young boy, Henry.  He only has a couple of lines.  Consider auditioning for that role too, if you can pull off a ten year old boy's voice.