It's generally considered best to introduce discus to a new tank first, before any tank-mates, to allow them to acclimate and become fully comfortable in their new surroundings for the first few weeks without having to be exposed to other fish during this period.
It's also better to undertake a proper quarantine with the tank-mates being placed in a QT tank (rather than the discus), to be later introduced to the main discus tank, as this creates far less stress on the discus.