Itinerary changed - advice please

Why have you not been sent the new itinerary surely that’s more of your problem are you on the same holiday as the friend could there be two different holidays running parallel?
Have you spoken to the church or other travellers to see if others have this different itinerary ?
Speak to the company organising it before going ahead of yourself and looking to cancel, well I would

A 50% deposit does seem rather excessive and I personally would have queried that initially.
As for the legal situation and lack of notification of changes to the itinary you best course of action is to contact the organisers at the church as soon as possible, the other traveller could possibly be on another trip to you.

I’d contact the travel company or your church first in case a mistake has been made