I visited Israel as a solo traveller earlier this year. I got some quotes from tour guides and found these too costly for a solo traveller. (I am aware this may not apply to you as there are two people travelling). My next option was to consider group tours, my hotel recommended a company (http://newjerusalemtours.com) that operates walking tours in Jerusalem, I joined one of their free walking tours of the Old City, it was excellent. The company also has a half day walking tour of the Mount of Olives, I'd taken this tour a few days later and would recommend it. Both times the walking tours had less than 10 participants. If you can't find a private guide, definitely consider this company for walking tours.

To get to Yad Vashem it's best to take a taxi, I found the bus stop to be too far from museum and the walk would be unpleasant in the heat.