Xbox Friends

I assume they all are in party, as he is in a group. Xbox friend can talk to PS4 friend and Xbox son can talk to PS4 friend. But in the same game Xbox friend cannot talk to Xbox son. Leaving PS4 friend to relay each of the XBoxs to each other.

I have the same problem on CoD MW and I have my the other Xbox player as an Xbox friend and in game friend but cannot hear each other.

Have you tried having him send you a friend request? This is some information I was able to find. It might be worth a shot to have him send you a friend request.

Viewing your Xbox One friends on your Xbox 360 friends list

With Xbox One, a friend is anyone whom you add to your friends list. Adding new friends on Xbox One does not require that they send a friend request first.

When you sign in to an Xbox One console, your Xbox 360 friends will automatically appear in your friends list, as well as your followers list. If you accept a new friend request sent from an Xbox 360 console, you will see them as a friend AND a follower
on Xbox One. However, friends who have been added on Xbox One will not automatically show up on your Xbox 360 list. If you plan to play with them on your Xbox 360, you’ll have to send a friend request through your Xbox 360 console. Once they accept, you’ll
then see them in your friends list on both of your consoles.

You mean...xbox go to friends...XBOX go to friends...XBOX go to FRIENDS!...screw it. *picks up controller*

For a friend to be a friend on Xbox 360, your friend has to friend you back.

If only you are the person befriending him, you become a "follower". Only if your friend adds you to their friend list on the Xbox One as well, you become friends.

I think that this link might be of some assistance.
Minecraft Realms

Hope it helps

Keep Calm & Game On!