1. Can 1k book saver award (NY) with miles from other account? My guess is no but doable if you find a helpful agent?
2. If I also find a flight with XY 1, NY 1, I assume I can book two saver award from different accounts (one is 1k)?

This Jan I helped my friend change his ticket (same routing, different carrier) and we did not pay any fee for the second time we call although I guess we was lucky.
(Miles come from his account but I made the reservation and pay tax+fee.)