Syrenne is auntie Syrenne. She's like the mommy of the group while Dagran is the daddy. They team up on missions and he can pretty much keep her reeled in. Syrenne hates men and loves drinking. Dagran is her drinking buddy, though he doesn't drink much from what I remember. She's also a bit reckless and needs bailed out. But she has Dagran's back and he has her. It's hard for her to trust men because where she is from women do everything and the men are pretty much worthless. At least that's how I understood it from her explaination. Syrenne also looks after Zael, saying "If you need anything, you just ask Auntie Syrenne." So if she treats Zael well, Dagran probably treats her well.
Lowell is the womanizer, who always flirts with Syrenne and anything else with boobs. Though Dagran trusts him. In chapter 25, I think it is. Dagran and Lowell's roles seem reversed. Dagran is fool hearty and Lowell is the tactics master. It's optional to do this, but it is odd because this only happens once. And because of Dagran's sacrifice, is why Lowell is able to keep going. Lowell later takes tactics role and Zael is the leader. Dagran had to have trusted him a great deal for this to have happened.