As long as I can understand, you will have a custom Android ARM board that will communicate to your embedded controller via RS485 or SPI. I said "custom" because AFAIK the standard Android platform/device usually just supports USB as a physical link. In the future, you plan to use a standard Android tablet/smartphone as a "console" so you will have USB communication only (or you will fall back to wifi or Bluetooth).
In this case, I think we can assume that you will end up using the Android Open Accessory Dev Kit at the end of your development process and will use USB as you physical link:
This will be a source of headaches by itself.
If you plan to develop for a few different platforms (mainly Android, Apple iPhone and Window 8 Phone) most likley you will end up using an abstraction layer like:
or any other one of these:
This will be another major headache.
Maybe you could evaluate a differente solution. Maybe something similar to AirDroid:
That is: put a small web server inside your embedded controller and use it to expose a web interface via wifi to any web-capable device out there. If you are using Linux, QNX or any other Unix flavor as your embedded system OS, the embedded web server should not be a problem.
This way you would have to develop just a single administrative web application to be hosted by your controller and an single web-interface for your clients. Please note that this client-side UI would not be a HTML5 wrap around the native mobile platform (like phonegap) but just a simple web page that could be seen and used by any web-browser on any kind of device.
Have a look at webmin for Linux, as well:
There are other, sometime better clones of webmin out there. Many of them are already used in DSL routers and other net appliances to expose a web interface via ethernet and/or via wifi.
To expose your embedded controller functionalities to the web-admin application you will just have to develop a few interface libraries (C/C++ to Perl/Python/Ruby/whatever). This can be done with tools like SIP and SWIG:
If you use a layer abstraction, like phonegap, put at least a couple of your most experienced programmers on it. This will be the hard part (because phonegap is the crossroad of all of the other problems). Ask them to develop a small, very simple app with it. It will take them a week or two but it should be enough to understand how to use the abstraction layer and how to solve the main problems.
Put one or two of your structured (C) programmers at work on HTML and CSS. This should be quite easy for them. Please note that they will not have to dominate CSS. They will just have to understand and use it in a quite basic way (at least at the beginning).
In any case, your real problem seems to be the lack of a senior programmer who already knows all of these technologies and can lead you in the design stage (and can solve the hardest problems during the development).
ORION is absolutely right in suggesting you to hire a consultant to play this role.