1998 Subaru Outback front brake calipers

Most cars are single-caliper pistons, with dual pistons on that one side.

Yousuf Khan

Dual pistons are used when the rears also use discs.

Single pistons are used when the rears are drums.

The OP didn't say what he has for his rear brakes. Yep, the 98s might've had rear drums; see:

The Legacy Outback got renamed to just Outback (starting first in Australia). The 1st generation of Outback is a Legacy-based vehicle. The Legacy wagon was the foundation for the Outback. The Legacy wagon got modified, and the Outback was designed by Olivier Boulay at Mitsubishi: raised roof, suspension changes for higher ground clearance, and bigger 2.5L engine. The Legacy Outlook was a Legacy wagon on steroids. The 2nd generation of Outlook (Legacy no longer in its name) from the 2000 model year, and on, was after the OP's '98 model, so the OP has an older Outback model based on the Legacy frame. That's why parts for his car are listed as Legacy parts, and why his "Outback" could have either disc or drum rear brakes, and that affects which type of front caliper is used in his car.

I think the OP must've misstated what he meant to ask. Don't remember seeing a vehicle that has 2 calipers per wheel. It's just 1 caliper. He probably meant to ask about single- or dual-piston calipers on his front wheels. To know means he has to crawl underneath to look at the rears to see if those are discs or drums.

He could also lookup by the VIN for his car. The subaru.com site lets you search for parts by VIN.

That the OP doesn't know his car probably means that he doesn't have the expertise to do the caliper, disc, and pad replacements along with a brake bleed or flush. Whatever car shop to which he takes the car to do the repairs will figure it out for him.