It is just the normal Dual wielding rule!
it is the same weapon on both hands so he has to use his Lightsaber skill and his attribute.
He has to choose one Primary weapon - only attachments on this Lightsaber that influence the pool are counted to the dice pool (the other hand is totaly ignored!! No 4 Boost by using 2 shotos with personal grip!! )
The diference of the attack by using two equal weapons is increased by one.
Since he has to use Lightsabers in engaded he has a basis difficulty of 2 +1 = 3
If he hits, he hits with the primary weapon, he needs two advantages to trigger the second weapons hit. (own damage calculation)
after he triggers the second hit he also can trigger all the other abilities of the two weapons.