Han Solo gets Lucky 1.
When Leia attacks, you may choose a unit that Leia can attack. If you do, that unit is also a defending unit for this attack, and Leia's attack dice are split and rolled separately (before damage prevention) between the defending units.
The chosen unit can be the same as the original defending unit for the attack.
The attacking unit is making one attack with two separate sets of attack dice. The attack against the second defending unit triggers attack effects.
The effect counts as a single attack against two defending units. Both units together will share each POP chance that occurs during an attack. (Including reroll, damage prevention, and discard.) Damage is done simultaneously.
If Princess Leia gets Double Strike, she may perform two split attacks, one split attack for each attack, thus she may affect up to 4 units.