A game subscription is tied to one person's account. That is why many families end up paying twice for the same thing, or the opposite: a child plays online on a parent's membership without anyone knowing if that is allowed. The good news is that all three console makers have a sharing rule. The bad news is that each rule is different, and none of them covers a friend who lives somewhere else.
The idea behind each rule is simple. Sony and Microsoft tie sharing to a console. Nintendo ties it to a family group of accounts. Once you know which one you are dealing with, the rest is easy to predict.
Pick a platform, then change where each person plays. The coloured bar shows whether one membership, bought by you, covers them.
On PlayStation you turn on Console Sharing and Offline Play on a PS5 (or set a PS4 as your primary console). Then other people who sign in on that console can use many of your PlayStation Plus benefits: online multiplayer, the monthly games you downloaded and, depending on your tier, the game catalog. Child accounts still follow their parental controls.
The limits matter. Sony says you can share with only one PS5 and one PS4. Cloud storage, store discounts and early trials do not carry over to the other users. And sharing with friends on their own consoles is not allowed.
On Xbox the setting is called My home Xbox. When you make a console your home Xbox, other people who use that console can use your Game Pass benefits, including games from your subscription. You can have one home Xbox, and you can change it only a few times a year (up to five). Online multiplayer is shared only if the Game Pass tier you own includes it, so check your tier.
Nintendo works differently. A Family Membership covers up to eight Nintendo Accounts, as long as they are in your Nintendo Account family group. The members can use it on the same Switch or on different ones, and family group members can even have accounts set to different countries. The buyer must be 18 or older, and if the person who bought it leaves the group, the others lose access until they join a membership again.
This is why Nintendo is the one platform where a family on several consoles, or a grandparent in another home, can be covered by a single purchase, as long as they are actually in the family group.
Sharing a login and password is not the answer on any platform. It breaks the rules, it puts the account (and its saved cards) at risk, and two people on one account will constantly kick each other out of games. Use the official sharing setting instead, and keep each child on a child account that you manage.
Also remember that sharing only helps if you actually play on the same console. If each child has their own console in their own room, PlayStation and Xbox sharing will not reach them, while a Nintendo family group will.
Before buying a membership for the whole household, run through this short list.