Originally Posted by Pilot37

If you have some doubt with regard to the return date of one passenger - I would brake the booking into 4 if you can (2 x 2 x 1-way tickets).
If you fly the outbound as a 1 ticket return and one person has to return on a different date - while the CS team can split the booking, if only a lower cabin is available vs what you originally booked, you won’t get any reimbursement of the Avios overpay as the trip has been triggered as active. If you book 2 x 1-ways - then you have the normal ‘up to 24hrs prior to departure protection’ to cancel the ticket and receive a refund.
I just suggest booking the whole trip as 2 x 2 x 1-way tickets because if you need to amend one - it can be all done online vs having to call CS if two people are on the booking.

Pilot37