How to get big-picture feedback from advisors, rather than just details, during fieldwork I am a PhD student in the social sciences and halfway through my fieldwork. It recently became clear that my original research project would not work out as planned and significant changes were necessary.

How do I elicit advice (via email or skype) from my advisors on which new idea they view as most promising?

I am corresponding with my advisors trying to develop ideas for new ways forward. My problem is that my advisors only provide comments on the details of my new ideas, as if we were at a workshop presentation. (e.g., I suggest two new ideas, and they respond with three questions/suggestions for each idea about how I could improve it.) I am grateful for this. But what I need most now is some guidance and what new ideas stand out. What seems promising/exciting and what less so. 

I know that my dissertation project is ultimately my choice, and should be driven by my interests, but I would like to make the decision with some outside guidance.
You need multiple mentors for different purposes.  In my experience, some very experienced faculty cannot see the big picture of their research, but provide excellent advice about the details.  Some similarly experienced faculty can only give advice on the big picture and will pay no attention to details.  Seek mentors with a diversity of strength.  

You can also try asking your mentors explicitly for broader advice.  I've had mixed results doing that.