Hi Anerol C
In March this year I was in the same position as yourselves. The board wanted one registration (9001) across three sites in diferent parts of the country. They did not want to know about cost savings etc, just wanted to get a streamlined company.
Anyway, in October the last site was assessed and we are now all under one registration.
I am based at the Head Office so started with the QMS we have had in place for the last 12 years. One site was registered to 9001 and the other was not.
Basically, the Quality Manual and procedures are generic across all sites and are available to all through the company intranet.
I did not want to change the world and get peoples backs up in the process, so I went along with the notion that 'if it a'int broke. don't fix it' I reviewed all site specific work instrucitons and documents and changed very few - they worked and the staff were used to working with them!
The easiest one was the site that had no QMS as we could implement the QMS from scratch.
Only observations were made at both sites.
My only advice to you I think is to get the staff on your side.

Try to make it exciting for them and take on board their ideas. We don't have a local champion as such - yes, some do more than others - but all contribute.
I am trying with auditing the sites at a rate of once every 2 months. Early days yet, but I think this is sufficient for the amount of employees and simplicity of the processes.
My next target now is to get 14001 across all sites. Next year looks pretty booked up then!
Good Luck!