Requirement for fire doors for HMO (for joint/single tenancy agreement)

HMO Licensing

I have 2 properties (both are 4 bedrooms and 2 storey), both have HMO licenses - one property is occupied by a family and the other is let on a single/ joint tenancy agreement to 4 friends that are working professionals - the question is - is it a legal requirement for the kitchen door leading into the hallway and the reception room in both properties to have fire doors for each property?

I note on the NRLA web page that where the property is let on a joint tenancy the new fire requirements  do not apply (i.e. fire doors are not legal requirement)  - www.nrla.org.uk/news/fire-safety-updates-in-hmos-what-landlords-need-to-know. Have I understood this correctly.

My concern is that when I was given my HMO licenses a couple of years ago and given some time to install these, I have struggled to find anyone to install these and get a certificate to validate this. I have requested quotes from tradesman on various websites such as Checkatrade but without much luck. Where i did get someone and had the doors delivered the tradesman got the measurements wrong and they had to be returned. The doors are not a regular size and are not easy to find and hence they either need to be made to measure or the walls/ bricks need to cut back which involves a lot more work and cost. The quote I got today and without a onsite visit for 4 doors was over £5k. 

Whilst I have installed hardwired fire alarms, have fire extinguishers, fire blankets etc  it would be really helpful to know if this is a legal requirement under the new rules, especially given the difficulty to find someone and at a reasonable cost .