Are they able to enter the world? I'm wondering if the world is corrupted and that's why you're not able to access it. Give me a bit more information. ^TK

This is kind of a pain, but what you could do is have your friend download the World and upload it to a new Realm. See if you're able to join that. May be corrupted but I'm not 100% since it's crashing on you and kicked you all out. ^TK