How to join a realm from console

[carmine garnet]

I dont think you can join sice they are on java

Select the Play button on the main menu.
Select the pencil icon next to your Realm's name.
Select Members. Your Xbox friends list is automatically available.
To add someone who’s already on your Xbox friends list, select Invite next to their name. To add someone new, first add them to your Xbox friends list. To do this, see:
How to add new Xbox friends
Once they've added you back as a friend, they'll appear on your Xbox friends list in Realms, and you can send them an invite to play.
You can also invite players with Realms invite links. These are custom URLs that are unique to your Realm. When someone accepts your invitation, they’ll be asked to sign in with their Xbox profile, and then they’ll be added to the Realm’s whitelist.
Note Only the newest version of your invite link will allow new players to join. When you refresh an invite link, anyone who’s previously joined will still be on the whitelist and can join the world, but new players can’t use that link to gain access.

that is from the support page

Have them follow those steps listed