Singapore Airlines KrisFlyer - On-line booking for connecting flight

Soon I will be flying from Bangkok to Cape Town via Singapore with SQ. I believe that I can check in online 48 hours beforehand. (This is part of a Star Alliance RTW trip)
Once the check-in opens for the first departure will this give me access to both the flights or just the first one. The most important one to be able to choose seats will be the Singapore to Cape Town. I don't want to check in for the first, find I can't access the second, and then find that I can't go back in to check-in for the second one as I've done the first stage.

You don't need to have flown the first flight in order to check in for the second. However you must have checked in for all previous flights on the ticket (eg if you fly to BKK the previous day on the same ticket you will not be able to check in for BKK-SIN until already checked in for the XYZ-BKK flight).

.......Once the check-in opens for the first departure will this give me access to both the flights or just the first one....

OLCI opens 48 hours prior to your flight based on each segment. You can check in for your SIN-CPT flight 48 hours prior to its scheduled departure time. This is not linked to your connecting flight.

You can do OLCI 48 hours prior to BKK-SIN flight and come back later to check in for SIN-CPT, or you can wait unitl 48 hours prior to SIN-CPT flight and OLCI for both. @:-)

Many thanks to both. It's the only leg of the trip where seats can't be pre-allocated. I'll now use seatguru, etc to see where is best for us to sit on the SKK - CPT flight. It's a honeymoon so there's so much to think about!