ABANDONED. Main characters dont age for some time

[Sinai]

I cant remeber anything about that book, and the year I read it in (2014) probably wont help much since i read it at school (7th grade). Its about "teens" that are stuck at their age for (i believe) 30 years (i think they are supposed to be 13 in all). They are looking for two girls (daughters of their deceased ex-member, if i remember correctly). They (the girls) are supposed to be sacrificed at some magical tree so that they (the teens) can get some sort of powers and be immortal.


(I really dont remember if this is of the same book)
One girl is being taken care of by their aunt, and she meets a guy at some sort of safe haven (for her, anyway), but it turns out he was sort of cheating on her with her identical twin, and they find this out when they go to a party and realize they have a twin.
*This book is called Balefire and I dont think its part of the first one.

[Lobstergirl, au gratin]

Sinai left the group. Moving to Abandoned.