Q:
Regarding Superior Sigil of Night
very likely not. The reason is that damage is determend on hit and is done with a specifick weapon. As you can only hit an enemy with a single weapon, the sigil on that weapon determines the effect.
Arise, ye farmers of all nations
Arise, opressed of Tyria!
Arise, opressed of Tyria!
just to clarify, if the sigil is on the offhand, its effects can still apply to main hand skills, so mercury that comment wasnt really correct. However, IF, you have 2 sigils that proc on crit, the mainhand one will be considered first, before going to the offhand if it fails.
Two permanent stat increase sigils will not work together. Read the wiki page on sigil rules.