Septuplets

I really believed that nasiens and his siblings are septuplets and are of the same age and the birth order is the only thing that identifies who is the eldest. If you think about it why does tioreh looks older than phao. And tioreh if she's just sixteen means that nasiens who is currently 18 tells me that if they are not of the same age then the current age might be Nasiens- 18 Sixtus- 17 Belte- 17 Zana- 17 Zillian- 17 Phao- 16 Toireh- 16 Or they coul be all 18 That's why nasiens became a victim of changeling plot