Some of you girls get way too antagonistic with your inlaws over non-issues. This is a non-issue. They are excited about your future babies because they will be a part of their family. That is not something to feel threatened by!
the problem is that they don't want to hear that you have plans other than making babies.
if you were still young and had plans for your life before kids and you had some aunties telling you to hurry up and have children before you're too old, wouldn't you feel a tad pissed off? it's not their business.