3) Krushinski/Krushinsky (Variant of 1b.?)
The "sh" shows those two variants to be Anglophone respellings.
You might have also added Krósiński and possibly even Krószyński. No-one spells their surname that way in Poland at this time though.
Krusiński is used by more than 800 people in Poland, Krusyzński by some 5,000.
Krasiński comes from a different root - krasa (beauty). The Kru- ones from kruszyć (to crush).