I'm upgrading my first gen braking system to TII brakes using a kit. Are all front and rear TII brake calipers dual piston?

I was looking on RockAuto under 1991 Turbos and noticed a variety of single and dual piston calipers.

Also, are some turbo calipers aluminum or are they all cast?

 

They're 4 piston in the front (two on each side) and single piston in the back.

They're all cast aluminum up front, steel in the back.

The single piston fronts are from base model s4s, you don't want them.

There also 2 different calipers in the back, I assume you want the one for vented brake rotors

 

just to add to the above, there are three different brake systems, and the TII brakes came on several different models.

the 86-88 4 lug cars get a single piston setup all the way around, its very similar to a GSL-SE brake system. the base models and the SE package have this, anything with 4 lug wheels.

the 89-91 base brake system gains the 5th lug, but its still single piston iron calipers, and non vented rear rotors. the 89-90 GTU model has these, and then its just the coupe in 1991.

so then everything else gets the 4 piston front/vented rear brake setup. this is the turbo 86-91, the convertible 88-92, the GXL 86-90, the coupe with A package, 1991. also the 86-87 sport, 88 GTU (but not 89 gtu!) the 89-90 GTUs.

canada is the same, except they call their base model the GX.

 

At Rockauto even though you've selected the turbo model it still lists the brake parts for all models so you have to sort through them all to find the ones you need. I think you look for the rears that say something like " with four piston front" or "with vented rear rotors" etc. to get the turbo parts.

 

to be clear, the single pistons are floating calipers and the 4 piston fronts are fixed.

The turbo models used floating rear calipers just like 99% of cars on the road.