This is a bad situation, but there are several points that spring to mind
- you are (from the context of the question) not this employee's manager.
- dobbing a colleague in typically doesn't result in a better workplace environment
- you are collecting information that you absolutely should not be
- you are spending company resources on unauthorised activity
- the boss's son is strangely competent from your one example
In this context, the boss is more than capable of turning around and saying "are we not hitting targets because of "Guy", or because you haven't been spending time hitting targets?"
That it is the boss's son is immaterial. That you've been snooping on a colleague is a pretty big breach of trust - the boss might wonder if you snoop on him! Colleagues not in the loop might wonder if they're being snooped on!
And when it becomes knowledge that you reported on "Guy" using this snooping as evidence - oh brother! What is morale going to be like then?
So to answer your immediate question, point 3 is a bad idea in the sense that it is unlikely to achieve its aims. On the other hand, it has the possibility of landing disciplinary action on yourself, and on reducing morale even further.
Point 1 is hard to answer because I don't know if the boss owns the company, or is an employee of the company. If he is an employee, where is he in the hierarchy?
As a rule of thumb - if he is the owner/high up in the hierarchy, then you should ignore this behaviour. Maybe look for another job, but don't report it. The son may as well be a proxy for the boss - it is the son's company, in effect. Even if the boss takes your side, the son won't, and you won't be happy with the situation later on.
Point 2 is a weird idea. If I wasn't working hard at a company, I'd probably know about it. It wouldn't be a revelation to discover. What would this achieve? Showing "Guy" the evidence you have is a terrible idea, because it is in fact evidence that you haven't been doing your job, and he is effectively your boss (by proxy).
It isn't going to cause a change, why would Guy change his behaviour? It will probably make him dislike you, and it definitely will increase tension in the workplace.
What you need to do is resolve the actual problem. I don't think the problem is the boss's son slacking off. I mean, that is part of the problem, but it's not a part you can really solve, so let's pretend it isn't the problem.
Instead, you need to solve the fact that the team constantly misses sales targets and deadlines. If anything reduces morale, it is being part of a sinking or otherwise underperforming ship.
Raise to your boss that the targets should be modified - to improve moral. Raise to him that perhaps more metrics need to be taken to determine ways to improve. The metrics aren't about finding out who is underperforming! They are there to find the best practices, and how to utilise them more fully.
This is a good way for you to show leadership. I know very little about modern day (or latter day. or any) sales theory, but there must be some processes that can be used to create measurable, meaningful data to analyse performance. Suggest you implement those, whatever they are. (This site might even be the place to find out what they are, but you'll need to word that question right to stop it being closed)
It might come out in the wash that the boss's son is... a wash1. It might not. But surely being part of a better performing team is what you want?
Fighting against what is the very concept of nepotism is a losing proposition, so if that is really what is bothering you (fair complaint, btw) I'd suggest looking for another company instead.
1: PUN* INTENDED.
*: Is it even a pun??? I find defining pun-ness tricky.