The UK Gov says all families should move together but I don't understand if they refer to a family with kids or a married couple without kids is consider a family and should go to the border control together?
The gov.uk website says
You must ... move through passport control together if you’re in a family
To avoid delays, when you arrive at UK passport control, please:
* stay together when travelling as a family
They don't define what they mean by 'a family'.
I suggest that you approach the desk together. If this is wrong then the worst that will happen is that the passport control officers will ask you to go through one at a time instead.