This is one of those situations that is likely to be ruled differently depending on the group you're playing with. While there's obviously going to be plenty of overlap in how some of us would rule, the thread clearly shows that everyone is going to interpret such a convoluted situation differently and then apply rules as they see fit, rules which themselves may be interpreted differently at any given table.
Of course that's all obvious, so on to how I'd rule it.
For me the key to this one is in how
I interpret and use the rules regarding invisibility and hiding. The invisible and flying PC never actually attempts to hide, at least not based on what I can recall reading in the OP. Because of this when that PC passes by the others they all know that there's some invisible, flying
thing passing them by. They might not know who or what it is, but they know it's there and more importantly they know specifically
where it is. Because of this the other PC can target the invisible, flying PC and dispel both spells. If Dispel Magic specified that it had to be a creature you could
see that would be a whole new ballgame, but it doesn't.
By the by, notice how my ruling has nothing to do with the wand itself being visible or not. This is because in scenario as presented it doesn't matter in the slightest. At least not to me. If the invisible flier had decided to try and hide than maybe the wand being visible would play a part... say maybe advantage for the other PC on their perception check to notice the flying invisible PC carrying the wand.
Anyway, what a silly game we all play...
