As for your first question (at least this early in the series) I don't think there will be any time travel. In the thread for Cuff of Cruce, I posted that Cruce has put a forbidden curse on the fae silvers. While they are able to sift place, I don't think any fae or otherwise are able to sift
time.
As to who planned Mac/Alina's adoption/exile? That is a million dollar question, I wish I had an answer for!

Was it to keep them safe or to keep them out of the way? Gabby's best defense in
Immortal was that she knew who/what she was. Mac not knowing who she is has not played in her favor much.
I think Rowena (old lady that rapped Mac on the head) will have a much more prominent role in helping Mac understand her heritage/power.
I don't know that I believe her adoptive parents know a lot of the girls heritage. - Unless they already had a full understanding when they adopted them - it might seem a little strange to hear "BTW, don't ever let them come back to Ireland unless you want them to be destroyed by Fae, Vampires, Werewolves, and other terrifing creatures." (but like I've mentioned before, I could be eating a lot of my words once the series progresses.)
I'm going to stop here because I'm writing a book. LOL. sorry guys!