I need some advice.

I live in a a middle of a Victorian terrace in a maisonette on a which has ground floor entrance, first floor kitchen, side door leading to garden via external steps, dining room and living room, then small bedroom with bathroom on second floor and then another bedroom two bedrooms on the top floor. The flat has benefit of roof terrace and sole ground floor yard garden with gate exit. This is owned by my landlord ("leaseholder")

The ground floor space occupies a restaurant (but does not share the garden as it's for sole purpose of the maisonette only). This is owned by the restaurants landlord ("the freeholder").

It seems as if the Freeholder is wanting to take the side fire escape steps away rear steps away and replace them with a juliette balcony. The leaseholder is fuming as they form part of her property, they are listed within the deeds of the property, they have planning permission, they've been in situ for 40 years. The leaseholder is seeking legal advice because they belong to her but the Freeholder is saying that they do not form a part of the lease demise, so the leaseholder is taking legal advice.

However I would like to know can someone take someone else property away and simply replace it with a juliette balcony? What are the rules on this? I feel like they can't be taken away as they are a fire escape. 

Depending on the layout of the building it may not have been added as a designated fire exit under Building Regulations and is just garden access - you are best seeking property law legal advice in the first instance

It has planning permission. The stairs were installed 40 years ago.