Clarity of HMO rules

HMO Licensing

My son has a three storey property and wants to let it to four professional tenants sharing,but on separate contracts. The property has three bathrooms and hard wired interlinked fire alarm. I believe this would constitute an HMO but does not have to be licenced?. A large well known letting agency has told him that because he is intending to use separate contracts he will have to have it licenced. I believe it is still the case that it is five or more tenants in three or more storeys irrelevant of the type of contract that require a licence. I believe the only other thing he would need to do is to fit a firedoor to the kitchen.?

Who is right?? The council guidelines as usual are not in plain english and not clear.