Illusions do not benefit from item raw damage or attack speed, they benefit only from item stats, i.e., int, str and agi. The only item effect that works on illusions is Diffusal Blade feedback orb, and this is for melee heroes only.

As for passive abilities, yes, illusions do benefit from most of these. For example, Chaos Knight's illusions have Chaos Strike, and Mortred's illusions (if one have Manta Style) have Blur and Coup de Grâce.

Illusions do not benefit from item raw damage or attack speed, they benefit only from item stats (int, agi, str) or auras such as radiance's or vladimir's. Note that they bestow the aura, but may not benefit from it, which is the case of the lifesteal aura from Vladimir's. 

The only orb effect that works on illusions is Diffusal Blade feedback orb, and this is for melee heroes only. Also it is worth noting that illusions get the critical chance from Daedalus/Crystalis, but not the raw damage.

As for passive abilities, yes, illusions do benefit from most of these. For example, Chaos Knight's illusions have Chaos Strike, and Mortred's illusions (if one have Manta Style) have Blur and Coup de Grâce.