We have enjoyed a lot your house. It is a tricky project, due to the multiple constraints, but also challenging. We have decided to give you 2 options : One that is more realistic, with the entrance where it is now, and the second option, with the entrance from the garden - if that is possible.
Version 1:
Kitchen is shifted to very beginning of the house, and integrated to the dining room and living room, but still with enough privacy and a small storage. In this way this integrated zone is big and full of light.
In order to use the long and dark corridor, we have divided it into 2 parts – first part that can be seen as part of the entrance and the living, with some bookshelves, coat hangers and drawer. One idea is to make a big opening in the living room wall towards to corridor, to give some more natural light there and connect these 2 spaces with some interesting ambient.
The second part of the corridor is dedicated to the sleeping zone, and is made of closed wardrobes and storage spaces.
The work desk is part of sleeping room but has a glass opening towards the corridor and the exit door so a lot of light.
Version 2:
If it is possible to enter from the yard, that would be an option that would suit your needs greatly – because all the rooms are bigger and with good light (in the previous option nanny/guest would have windows to the neighbours)
Dining room, living and small study corner are part of one big space. Kitchen stays where it is now, which is quite functional in this case, you will not have expanses to move the pipes and it works well with the dining.
We hope you like the versions and will be able to use it and enjoy the space!