Hello,
If there are four seats available then you go for it, before someone else does
If the moon crashes into the ocean and by some freak someone then magically makes real bookings on the same flight you can always refund the 2-4-1 booking for a small fee and total return of miles and voucher.
For belt and braces peace of mind only you could call the BAEC and do it over the phone, but you'd probably incur booking fees per-person.