a. Let me know whether you’re happy with this or you would like any changes to be made.

b. Let me know whether you’re happy with this or whether you would like any changes to be made.

c. Let me know if you’re happy with this or if you would like any changes to be made.

Which is the most correct version here if any?

Which is most natural, and which would you use?

Cheers
This is my opinion:

b. Let me know whether you’re happy with this or whether you would like any changes to be made. is the most correct version of the three examples you offer

c. Let me know if you’re happy with this or if you would like any changes to be made. is most natural of the three examples you offer

d. Let me know if you are happy with this or if you would like any changes is what I would use

Which is the most correct version here if any?

Which is most natural, and which would you use?

Cheers
Hi,

Does this mean you see a as incorrect?

Cheers
Students: Are you brave enough to let our tutors analyse your pronunciation?
You asked:

“Which is the most correct version here if any?”

My response was that I felt that "B" was the most correct of the three versions you proposed. It's not that I see "A" as incorrect; it's simply that I feel that "B" is more correct.

You asked:

“Which is most natural …”

My response was that I felt “C” was the most natural of the three versions you proposed.

You asked:

“… and which would you use”.

My response was that I would not use any of the three versions you proposed.

I would use:

“Let me know if you are happy with this or if you would like any changes.”

Often, it is more a question of stlye than grammar. I have always preferred an uncluttered, simple but elegant style.