Buddhism may accept Jesus as a 'prophet'.
Judaism already has done so.
Muslim already do as well...
I need more information about this 4th group to find their doctrine and learn.

As for doctrine outside of this one holy person... I can say that nuances make a huge difference and history has not provided soluble coincident terms for joint acceptance of these differences that I have seen.

If the goal is to make one religion that suits all, they may find that most will dislike dilution of doctrines. And some may take offense to any dilution.

To me:
- Chocolate is awesome
- Vanilla is quite tasty
- Strawberry is nasty
- Coffee is the bomb
Likely I will not like the grey result of their mix.