Odd two S1 O2 sensors went at the same... make sure you don't have another issue. Remember, the OBDII codes for O2 sensors showing fault only means their values being reported are outside of norm...not that they specifically are bad. Did you test them w/ a DMM first to ensure they are bad?
As for replacement... yes usually easier when they are warm. They should have had (and the new ones too) a touch of anti-seize on threads when installed. Otherwise, pretty straight forward (assuming you have the crows-foot or equivalent O2 socket/tool).
Good luck