LHA - Second bedroom for a Carer

I’m sure this is really quite simple but I just cant seem to get my head around it.

I have a client with learning diffs who lived in a a house which his father rented. His father naturally acted as his carer. His father passed away recently and my client’s sister and her husband intend to move in and live with him so that they can be his carers. The landlord has offered my client the tenancy.

He is on DLA so there should be no non dep deduction but what about the amount of LHA he would be entitled to - would he get the rate for one bedroom or one bedroom plus another for a carer? His sister and her husband will not have a separate address after they move in so it is not comparable with those situations where carers come and go on a shift system but it is nevertheless the case that the only reason his sister is moving in is to look after him and by any reasonable standard she must be judged his carer (she has applied for CA already). Any thoughts or experiences gratefully recieved and if it is obvious to everyone but me then I apologise in advance!

ps The landlord might be persuaded to offer each of them a tenancy, eg one for the couple and one for my client , but wouldn’t this mean that the house would become a multi occupancy and the landlord alone becoming responsible for the Council Tax?

Just to add….

Assuming the DLA is for care, I agree there will be no non-dep deduction.  However, even if DLA(C) is at middle or higher rate (presumably it must be for CA to be claimed), there will be no Severe Disability Premium - due to 1)  the additional occupiers and 2) if paid, someone getting CA for the clmt .

Thank you both for your replies, I think I have got so used to things being complicated that I am starting to look for complications where there aren’t any!

if he has learning difficulties, does he have legal capacity to enter into a tenancy? (just to put the cat amongst the pigeons…. but surely an important point!)