Coding-Decoding

In a code, each letter shifts 2 places forward in the alphabet (A→C, B→D...). Coding "WY", Disha thinks the rule breaks down at Y, since only Z is left after Y, not 2 letters. Her brother says there is a clean answer for this too — the alphabet wraps back around to A once it ends. Who is right?

In a code, each letter is replaced by its "mirror" letter — A with Z, B with Y, counting equally from both ends. Coding "B", Manav thinks this is the same "shift 2 forward" rule, so B becomes D. His sister says this is a completely different rule. Who is right?

In a code, "CAB" is written as "6". Om thinks this is "number of letters × 2" (3 letters × 2 = 6). His sister says the real rule is different — each letter's alphabet position has been added up. Who is right?

In a code, "CAT" is written as "TAC". Kaveri thinks this clearly shows the whole word is reversed, so she writes "DOGS" as "SGOD". Her friend says this single example cannot decide that. Who is right?