1)
Alfa Romeo
Dacia. Don't know anything about them, sounds sort of right.
Lancia
=FIAT

Opel
=GM

Audi
Bentley
Bugatti
Lamborghini
Seat
Skoda
=Volkswagen

Rolls Royce
=BMW

Rover.
=Changfeng? Sort of guessing, not sure anyone owns them anymore.

I think Lada is partnered with FIAT, but I'm pretty sure they're independant. I'm not sure about Lancia, every once in a while I go and look at what models they're making now, and none of them seem at all interesting. I wouldn't be suprised if they were owned by VW, but I think it's FIAT.

2) Vectra, I'm pretty sure.
I didn't know they were still making Omegas.

3) Chrysler Viper I know. Probably the Neon, maybe the Stratus? Chryslers must not sell very well in Europe. The Avenger doesn't seem to sell well even here, I don't think they'd have bothered shipping them over.
Chevrolet is really a budget brand in Europe, I don't think they'd have made an Alero.