This is a bike you don't know and a type of bike you don't know. I suggest you ride it a fair bit before investing in changes. It might not need changes. My spouse and I ride a tandem. It has two regular cantilever brakes. I was concerned that they might not be enough but they absolutely are. Maybe it helps that we are both lightweight, with a total body weight of 270 pounds. Even if we were heavier, our brakes would suffice. And we have ridden in hilly country.

I got the tandem in hopes of equaling us out since I have more stamina than she does. Making the pedaling easier should help her last longer in the saddle. Well, it does even us out but not in the expected way. Handling the bike is hard for me, especially my arms and shoulders. I have less stamina on the tandem than on a single bike. But you may not have that experience. I know I need upright handlebars on a tandem even though I like drop bars on a single. Drop bars on a tandem are terrifying for me. I guess I have weak shoulders.