Originally Posted by
kryten22uk
You don't "have" to book as singles if you don't want to. You can phone up and book all as one PNR. Then just ensure that they're waiving the offline booking fee because it was not possible to do online.
There's some advantages in keeping the bookings as 2 PNRs. This makes it more flexible to change the return leg after the outbound leg is flown. Or if you spot a sale cash price at the last moment or want to change your routing etc.
The main reason for having one PNR is to protect connections, and in an esoteric way that may apply when there's several days gap between outbound and return, but generally it won't be an issue.
So it may actually be best to keep them separate.