It's worth getting in touch with the school to talk to someone directly.  When I attended many years ago, the dual degree option simply gave you the opportunity to pursue two degrees at once.  However, they were offered by different departments and in no way integrated.  A friend of mine was accepted to the dual programme but decided against it after one semester.  I  also had some friends who did the dual degree with Construction Management which was also entirely separate from the architecture school.  You don't need the MArch for your license, why not consider doing a specialist Master's?  This would be shorter, give you the degree, and add a specialism?

You may also want to consider a specific Real Estate degree instead of an MBA.  Something that is particularly common in the UK for example.  There are very good part time programmes (look up the one at Reading, for example).  Which may be of interest to you if you are interested in learning more about the business side.  This would allow you to keep working, and even with flights, may be less expensive than a US degree.

Good luck!