Can I access DLC on a Home Console purchased by a secondary account?

This actually clears things up for me. Thank you Theory of Game.

I would think you would be able to access it, provided that your Xbox One is also marked as your son's Home Xbox. For clarification, each account can only have one Home Xbox, but a single Xbox can be the Home Xbox of more than one account.

Okay, here's what the OP can do...

1: Add his profile to his Son's Xbox.

2: Open a secondary account on his own (home) console.

3: Have his Son sign into the OP's primary account in the background.

4: The OP signs in using his secondary account.

That way the OP has access because he's on the home Xbox and his Son will have access because the account that purchased the game is signed in on his console. BAM! Problem solved.

Sharing a gold subscription on one Xbox One console is true, however a gold account can access their games on any console. Set one console as the HOME console under settings. This will make that console shareable with secondary accounts. To play together
the secondary account must be logged into the HOME console and the Gold account must be logged into the second console. At least that is what i have come to understand.

If by the "Shared with Gold idea" you mean the "Home Console" feature, where an account designates a specific console as their "Home Console", which then shares their Gold membership and purchased games with other accounts on the console, then you already
know how it works:

An account buys games DLC and Gold memberships, and as long as the console is set as this account's "Home Console", all other accounts on that console can play that account's games, DLC and play multiplayer with the shared Gold membership.

If you buy a game on disc, then the disc has to be in the drive to play the game. DLC that you get via a code, is bound to your Gamertag, and through the "Home Console" feature, others on that home console can access the DLC content as well (usually. I have
heard of CoD Season Passes being ONLY for the individual that bought them, and aren't shared, but I don't play CoD, so I can't verify that).

You can switch the underlying Microsoft Account email of your Gamertag, and since the purchases and code redemptions are tied to your Gamertag, you will keep your purchases.

But you shouldn't create a new Gamertag. Use the Gamertag you used on the Xbox 360, since your past purchases on the Xbox 360 can then be accessed through the Xbox One Backwards Compatibility. Only change the Microsoft Account email that you use to sign
into your Gamertag by creating an alias.