Anxious about consent to alter!

[MH0084]

Hi,
Just to vent, I guess.
I live on a garden-flat and co-own the freehold with upstairs neighbours (just 2 flats). I have sent them an email few days asking their consent for some structural alterations at my property (basically creating an open plan kitchen and living).
I'm losing my sleep over the possibility of them not agreeing to it, specially as I have already invested a lot of money on architectural drawings and all sorts of fees. The works do involve significant structural changes, but the team working on the drawings was extremely conservative and we are reinforcing foundations to way beyond necessary and have also added significant works to attend their requests which will cost me a lot as well.
They have now been radio silent and are ignoring my messages related to other topics.
I know I have to wait for "reasonable time" before freaking out completely, so I guess just wanted to vent!
Thank you for reading!

What does ‘added significant works to attend their requests’ mean please?
Is it a house that has been split into 2 flats, or a purpose built unit?

They said they would only approve my renovation if I improve ventilation in the kitchen as they complain about cooking smells, so I’m using a very expensive super strong fan, which I wouldn’t otherwise. But the most relevant one is the sound insulation beyond required by building control and this is costing me north of 20k.
It’s a purpose built victorian maisonette.

It would be so out of order for them to demand you put in extra bits and changes only to turn down the approval! Are they the only signatories required?

Is it only that you have ask them for their consent? Is that a formal legal procedure?

They might be joint freeholders in a Victorian conversion.

Edit: in fact they are, OP says so in her post. Leaseholders can’t make changes to the property without consent from all the freeholders. She is one, the neighbour is the other. Both have to agree.