I would strongly recommend you post this in the legal section,
However my limited experience of such cases would suggest that your offer is a very fair one on the basis that you have contributed more over the last 7 years.
On the subject fo the mortgage and house deeds......firstly the deeds will be held by your mortgage lender so that is not an issue.....with regard to the mortgage, so long as your income/credit worthyness is sufficient to support the mortgage in your own name, then you should have no problems at all. As far as cost is concerned...there will be some administration costs with the mortgage company and possibly some legal ones too...i would set a couple of hundres piunsa to one side....but also factor this in to the settlement to your ex.......y should u have to pay for it all!!!!!!
I hope this helps a little....and bye the way...sorry to hear about the split