Stamp Duty on Block of flats

I have a client (IOM company) which wants to buy a block of flats (6 individual flats) from another company (also Offshore, not IOM).

The flats are currently short-term lets and will remain so with the new owner.

I assume that it will be treated as 1 transaction, rather than 6 due to it being the same purchaser and same vendor.

But will it be classed as Residential or Non-residential? (HMRC lists six or more residential properties bought in a single transaction as being a Non Residential transaction)

I know the rates are the same above £250k but the value may be less than this