Two Couples So Four People - Is this a HMO

I live in a council which has licensing for HMO so that three people in two households require a license - Lambeth council in fact

Do I need a selective HMO to rent to

2 couples who are married / in a relationship?

I am sure the answer is yes but my agent insists not needed (However three students would need it apparently!)

A house in multiple occupation ( HMO ) is a property rented out by at least 3 people who are not from 1 'household.

So yes, it would be a HMO

Unless at least one member of couple 1 is related to someone in couple 2, then the property requires an Additional HMO licence, (not a Selective Licence).