Expat Wills overseas

Throughout our group of companies, some of our British and non-British non-Muslim clients live, work and have assets in UAE.
I find the laws regarding Wills in UAE confusing.

The Emirates have 7 states –

  1.  Abu Dhabi (which serves as the capital)
  2.  Ajman
  3.  Dubai
  4.  Fujairah
  5.  Ras al-Khaimah (RAK)
  6.  Sharjah  
  7.   Umm al-Quwain

Could anyone provide guidelines as to what is acceptable in each state please?
I am aware of DIFC (Dubai International Financial Centre) Wills and Sharia law regarding intestacy which, of course, applies to all states.
As I understand it, a DIFC Will is required for resident expats with assets in Dubai and separate Wills for assets in other countries.
DIFC charge AED10,000 for a single Will and AED15,000 for mirror Wills plus costs if they draft them.
The other states’ requirements are unclear. (I believe RAK may be the same as Dubai in the near future.)
My aim is to create a fact sheet which we can send out to our clients when we are advising them, which they can follow.
I would really appreciate your help.