Thank you all
Well, I haven't sign any contract yet.
And any information could help to draft it properly.
And also, its true, its done in a very amicable way.
It's funny. My "wife" got recently divorced and they used the same sollicitor which was his. She had not problem at all in claiming her share of the house and whatever she asked for.
Sorry about bringing up the fact that is a leasehold too late.