I would no do any wall washing. That is not even the type of chore a nanny would do if she did agree to housekeeping., unless it happened on her watch. Your employers sound really gross. You need to consider whether you are well suited to work in their home. Was it dirty when you interviewed?

The MB I'm working for just for the summer (thank God) is disgusting. I only work two days per week, so during the four day span of time that I'm not there she will just let unrinsed dishes, laundry, etc. pile up. She always asks me to do the dishes, so I do, but only because I know I won't be working for her for very long.

My main family that I work for never leaves a mess. MB works from home, so she will usually vacuum and sometimes steam the floor if it's a mess. The only real mess is from the baby's toys. I think she asked me to do dishes and clean up a little bit once because she was going to be out of town for three days, but that's about it. I also helped her organize the house once while the baby napped because her MIL was planning on visiting.