Multiple Apartments

I have three apartments in the same location. 

Apt 1 3 bedrooms- 6pax ( I created this unit first)

Apt 2 3 bedrooms 9 pax

Apt 3 3 bedrooms 10 pax

Therefore I would like a combination of them to show for larger groups, eg. for 15 pax Apt 1 & 2

I think I may have created them separately by mistake but the info on BDC is soooo difficult to understand

They are currently listed separately so don't seem to display together - I may have created them incorrectly.

Any ideas how I resolve this? Can I link them?

Or do I need to start again by adding Apt 2 to Apt 1 via property layout and then snoozing the Original Apt 2?