No virtual machine is bullet proof. They all have bugs and issues. Would you want to be responsible for encouraging someone to take a risk that ended badly.
You could teach this young gentleman how to segment his network "with his dad's permission of course" then show him how to circumvent as many possibilities of breach as possible, and how to shut down connection during testing to contain it, but seriously, what's the point.
Many malware are "sandbox" aware, and won't run. A good majority of them require Internet connection in order to transmit or drop payloads. On the other hand being responsible for turning a malware loose on a network or worse yet a server is no joke either.
The tighter you restrict the testing environment for safety the less effective it is. It bares responsibility also of not effecting/infecting others.
Creating a real isolated lab is more then just deploying virtual machine with vulnerabilities.
To the young gentleman: I would stop messing around altogether in your family's network, it sounds like your dad works hard to spoil you, show some appreciation by not bogging his internet down with all this crud and definitely stop taking advice from those that are trying to encourage you to be risky. Learn some better habits as well, there are users here "cough,cough" trying to reinforce those good habits that keep users from having trouble in the first place.
P.s. I told you once before, if you want to learn about malware and it's behaviors "reading" about them is more effective then playing with dangerous live samples.