This would be detectable
Prying Eyes creates a few small, visible, magical orbs.
Each eye is a Fine construct, about the size of a small apple
The eye would not automatically fail any kind of saving throw, even when they have no bonus to saves. They can however voluntarily give up that save, so that part will work. 1
While they have a +16 hide modifier, they are by no means undetectable. They are not even invisible. So the no way to be aware of it part of your question is not airtight at all.
Scrying only works on a single creature, so you could scry on a single one of your eyes. However, keep in mind that you can only
see and hear the subject and the subject’s immediate surroundings (approximately 10 feet in all directions of the subject)
Especially if you want to keep the eye hiding, it may be very difficult to get within 10 feet of your target at the same time.
So I think your stratagem does not do what you hope it would. In addition, the eyes are rather slow, and scrying is rather short lived, so you need to get close to your target, to begin with, before you even can try to get it to work. And you are buring two level 5 spells on this - I'm not sure that is a particularly great use of resources. I'd just let the eye spy on them and report back.
Or, I would recommend you use the Arcane Eye spell instead, unless you need to hear. That one is invisible, can travel as fast, lasts as long as your combo, also gives no saving throws, and only uses a single, level 4, spell slot.
1 There is the question if the Fine constructs count as creatures, and even can be targeted by scrying. The rules for Types say:
"A construct is an animated object or artificially constructed creature.
And animated objects have wisdom scores and are creatures, too, making all the options creatures. Here however, no Wisdom scores are given, which would by default make this construct an object. It is therefore ambiguous, if these constructs are creatures at all.