I thought about Antlers talking with the kids, and think it's OK as long as they are doing most of the talking. There is a fine line between letting the kids have a say and getting them too involved in matters that two adults should be handling with maturity and reason.
Antlers: Have you and your W worked out a schedule with regard to visitation? Two weeks is a very long time.
I know that you *heard* that you W was planning on bringing the kids to the grandparents house for 2 weeks, but this is HERESAY. You cannot assume that it's true until you tell her that you heard this information and get verification from her on it.
Overall, expectations with regard to visitation, holidays, and vacations need to be set before either of you make any plans.
You need to come to an agreement with your W so the kids don't have to be dragged through the undercurrent of push/pull!