Use of "only" and word-order

Only the Volkswagen Polo, Golf, Passat, Passat CC and Sharan are available in this country.

This could be clearer. Although common sense says otherwise, this sounds like these are the only cars available in this country. You might instead use

The only Volkswagens available in this country are the Polo, Golf…

If the article is clearly just about VWs, though, you could probably omit Volkswagen from the first version and be just fine.

For the Subaru Legacy, all three options convey the same meaning.

Only the sedan version gets the 1.6-litre/124bhp and 1.8-litre/132bhp engines.

This means that the these engines come in the sedan version and are not available in the wagon, which may not be what you want.

The sedan version gets the 1.6-litre/124bhp and 1.8-litre/132bhp engines only.

This means that these are the only engines available in the sedan (presumably others and perhaps these are also available in the wagon).

The sedan version only gets the 1.6-litre/124bhp and 1.8-litre/132bhp engines.

This means something slightly different. Here only suggests that something is disappontingly lacking, like we might hope for better options, but these two engines is all we get. This use of only is similar to this

I wanted the 2010 Audi R8, but I could only afford the 1988 VW Rabbit.