I agree that does not appear immediately as a 4 bed house. Much more needs to be made of the extension having a shower and toilet next to it - I only spotted it really after someone else mentioned it. It did not jump out at me in the plan.
The floor plan has also been badly done as it is not clear that the bathroom under the stairs is the family bathroom. But I am not sure what you can do about that.
Otherwise, while your home is clean and tidy, it looks like you've taken the 'home' out of the house. The front is tidy but bare - maybe move some of the planters down the side to the front of the house, park the car off road when the photos are done. I know it is your parking space but people don't want to think about actually parking under their front window and you have highlighted it here.
The garden photos do not do it justice, it's like they are an afterthought and I would want to see the whole garden, even if it has to be done over 2-3 pictures.
Overall, I can see that downstairs has a reasonable amount of living space. But I agree that it appears soulless. I know there is the theory of removing all personal items from a room when selling, but removing too much is just as bad, people want to be able to imagine themselves in that room and not having the odd picture on the wall, couple of ornaments on the shelves stops people from imagining themselves there.
Personally, I think I would switch some of the rooms around. The small upstairs bedroom I would turn into a home office and put one of the children's rooms in the downstairs reception bedroom, even if it's just for the sake of the photos/while you are selling the house. People won't always equate the room they see in the photo with the room on the plan so while it might seem deceptive, it shows 3 bigger bedrooms and one office space which is more useable.