Planning law + HMO licensing

HMO Licensing

My client has an HMO with 2 tenants who are a couple at present, the male wants to move his sisters in, no real objection to that they are relatives but they would sign up to another tenancy agreement and have their own room or rooms but they are all related, this would put the occupancy up to 4. My client has a letter from the council "intent to grant a licence" which we are waiting for confirmation of its granting. She has planning permission to use the property as an HMO. Does she need anything else. I note that the new planning law seems to say no more than 2 people sharing against the 5 under the HMO licence rules. We are both a little concerned but basically want to know if it will be ok to move the sisters in and that we are not in breach of any law whilst waiting for the final licence endorsement?

The planning permission to use as an HMO was granted last Nov.

Kind regards,