2 xbox one S digital only and 1 gold membership

ideally you want each of them to have there own accounts, if he is using your email account for xbox it will be very problematic in the future when he wants to take it with him as nothing can be transferred.

for now

make her a microsoft account and have you as the parent account, and sign in on the new console, then sign the other account into that new console and make it the home console, so when she is using her account she will have gold/gamepass access too. on the original console your lad can use it like normal but must have an active net connection all the time.

only set the daughters xbox as the home console.

It would be best to create a separate profile for her as once she gets older and does want her own account, there would be no way to transfer any of her progress to a new account.

You can share Gold/games with the use of the Home console setting. https://support.xbox.com/en-US/help/hardware-network/console/my-home-xbox In order for your daughter to be able to play the games on your son's account, your son would need to set her console as his Home. The Gold is what gets tricky. You can only have 1 console set as your Home at a time. So if the Gold is currently on your account and you have your son's console set as your Home to share with him, he would lose access to Gold if you set your daughter's console as your Home. If the Gold is on your son's account, then it would work the same as the game and you would set her console as his Home.

So I just re-read the link you provided, Danno, for the umpteenth time. (news.xbox.com/.../xbox-one-digital-games-and-live-gold)

They basically say that anyone that uses your X1 will have Gold access. But the question is, what if you have more than one X1?

We currently have 5 Xbox 360's in the house. Along with that we have 1 Family Gold and 1 Gold Membership.

When the X1 comes out, does this mean that when we get 5 of them we only need to use 1 Gold Membership for all to play online? (As long as that one membership is the "owner" of all the X1s, of course.)

Unfortunately, that page does not go into detail about this. It only talks about having ONE (an) Xbox One that everyone in the home can play on....not multiples.

Buy 1 xbox one with free FIFA 2015 includes as a digital game, but one xbox one with COD included as a digital game and then setup digital sharing, you also only need 1 person with gold membership. (The games have to be digital for this to work)

Unfortunately, you don't describe which account has the Gold membership and how the "Home Consoles" are set up.

Let me give you a bit background knowledge:

Memberships and digital game purchases are tied to the user account that purchased the membership or digital game download. This "owner account" can go on any console, sign in with his account, and as long as this account is connected online, they have their
Gold Membership and access to their games.

This "Owner account" can designate one single console as their "Home Console" as "yFoX inSanuS" describes above by going to the Settings and under "Personalization" define that one console as their "Home Console".

This setting will then share their Memberships and Games to that console. Which means: Anyone playing on that Home Console can play all the games and benefit from the Gold membership of the "owner".

So let's say "Grandchild1" owns the Gold membership, and "Grandchild2" doesn't. They each play on "Xbox One console 1" and "Xbox One Console 2" respectively.

So Grandchild 1 with the Gold membership signs in on the OTHER console (i.e. Console 2, owned by Grandchild 2), and sets Console 2 as their "Home Console". This Console 2 now shares Grandchild 1's Gold membership and games to anyone playing on Console 2.

As long as Grandchild 1 is connected online on any other console (i.e. his own Console 1) he still has his own Gold membership and Games.

BEWARE HOWEVER! The Home Console setting can only be changed 5 times during 365 days for every account! So don't change the Home Console setting unnecessarily.