Linked or Family Account and Benefits

I have two different accounts. One is a regularly used account that is currently in subscription and the other is a starter account, which is the one I am posting with. I have questions about how these linked accounts work and what it will do to help me if it does at all. I am a minor of another and was wondering how it would work to link this account with my guardian's.

1. How do I link this account to theirs?

2. Does this grant any subscription discount or benefits or any bypass to buying the expansion packs that a completely new buyer would be required to have?

3. Would this allow me to be able to play my character alongside the other account?

For better context, I have been looking for a way to play on my character and also allow my guardian to play on his other without interference. I have also been hoping that by having a linked account that the subscription would possibly carry over to the next or provide a subscription discount.
No discounts, no - every license is independent.

You could have a license on their Blizzard account, but it is actually much cleaner if you don't.
Leaving the accounts separate will help you when you want to split the account off in the future when you turn 18.

All achievements, transmogs, mounts, heirlooms, toys, pets, and pretty much anything else you can think of is linked to the battlenet login.

This means that anything you may acquire will pretty much be gone when the account gets split later.

This is why two separate bnet logins are recommended.