I believe you will need a a sub for each PS if you want them to be gaming online at the same time.
Just had a quick search and come across this from another site.
- Yes, everyone needs their own PSN account, if they want to play.
- Yes, he can use sub account from your account on another console.
- Generally he would need separate PS+ subscription, as well as his separate games, but there is a "trick", one might say, to allow your PS+ and games to be playable by him, but there are some tradeoffs.
- You have to deactivate your account as primary on your PS4.
- You add your account on his PS4, and set it as primary console. This will make your PS+ and games available to all accounts on the console, including your son's. There is major but though.
- Your console is no longer primary! Which means, you can play all your games and use your account online (PS+), but ONLY when you are online. Other accounts on your PS4 cannot use your games and PS+ either. The moment you are offline, or PSN is down, you will lose access to all your digital games.
- There should be no issues with playing eachother, other than what was described in 3.3
Also found this:
I'm pretty sure that to get 3 consoles online at the same time, you will require 2 PS+ Subscriptions at least.
Console 1, 2, 3
Accounts
A with the PS+, (B, C without)
Account A which has the PS+ can be loaded onto any console and reap the rewards of PS+
But Account A can only be a Primary Account to One Console at any given time.
Other Accounts that are on the console can take advantage of PS + and it's content.
Works well with 2 Consoles as you set the one Account that has PS+ to Primary and you can add a second Account, which in turn can use all the benefits of the Primary Account. You then just add the Account that has the PS + to the other Console as PS+ follows that Account to any Console.
As you have 3 consoles now, (how jealous some people are now), will result in having to buy another PS+
Looks like 2 Subscriptions for 3 consoles, the price of being greedy LOLz
And looking at what the Primary Account can share, you may have to buy 2 games/DLC to run 3 consoles as well. As only a Primary Account can share content.
For 2 Consoles, it works perfectly.
For 3.. [Console 1, 2, 3]
1. [Console 1] has the Primary Account (PS+) and is used by Player B with their own Account.
2. [Console 2] has the Primary Account that is created as a Non-Primary Account
3. [Console 3] has to buy Subscription and games/DLC