Does your agreement contain some verbage about if the parent that has the scheduled time with them isn't able to be with them, the other parent has first chance to have them before another relative or babysitter is called in? Mine does.
No, each parites time is exclusively theirs.
Me 35/XW 33 S13 & S12 M: 10/17/98 OM & S: 07/08 D final 06/09/09 12/03/09 - 06/13/10 "Piercing" 06/13/10: Engaged to Re-marry 10/17/10 06/25/10: Expecting baby #3 2/14/11