no, 1 and 8 are not on the same coil.
roughness is a rolling misfire count. each increase is an actual misfire, but this doesnt count as an actual misfire event until you have a certain number per minute. i think roughness has to reach ~10, if i recall correctly
however, the firing order is 1-8-4-3-6-5-7-2 so if 1 and 8 have more misfires than the rest then this might be something you feel.
you can measure the resistance of your plug leads, make sure it doesnt spike as you wiggle each end.
from the manual;
This (roughness) value will increase the more unevenly the engine is running. Engine roughness is not displayed if idle.
When the ECU detects a possible misfire, this count value is increased by one. If the value increases to more than
a preset limit within 1000 engine revolutions, a misfire fault is set. If not, the misfire count value will be cleared to 0 and a new count begins. It is normal to expect a certain number of 'false' misfire detections during each count.
that said, if the coil, leads and plug are good then you're left with either a valve problem or cam wear
the coil is good because you dont have corresponding roughness on #5 or #6 - wasted spark system
