so "at veje" means to weigh, if that helps you remember this one. I think of weighing something "over" a long period of time, it kind of works.
Why is the First V in overvejer pronounced as W and the second V pronounced as V?
Seems that V's at the start of a word are pronounced V. Vejer is a word, hence a V.
Whereas V's in the middle are like a W. Over is a word, hence the W sound.