First of all, there is only one sun – ours. Our sun is a star, other planets circle a STAR not a sun. „Sun“ is a name we gave our star. The same goes for moon but I’ve given up that fight because very, very few people call them satellites, which is their proper name.
Quite an alarming number of science-fiction authors make their different worlds exotic and different from Earth by giving them more than one sun. Typically it’s two. Here is why that is highly unlikely: Only a very small fraction of known planets are in what is called the Goldilocks Zone. This zone describes the narrow distance from a star that is neither too hot nor too cold for liquid water to exist – at the moment we cannot imagine life without liquid water. For life to exist and human life to be able to survive (and the running thread of these books is generally humans being introduced into a new ecosystem) there also has to be an atmosphere – without it we’d all burn and couldn’t breathe. An atmosphere like ours is incredibly vulnerable. A planet circling not one but two suns just wouldn’t have the constant environment needed to enable either liquid water OR an atmosphere. Also the two stars combined would have quite the gravitational pull, sucking in any planet coming too close. One book I read had three suns – I’m not sure that even exists. Because those two stars wouldn’t be sitting there in the sly being surrounded by planets, they would also circle each other in a circular to elliptic motion – three stars would likely collide and oops! Say goodbye to that planet!