Which of the following sentences is grammatically correct?

The correct answer is Option (3) → You, Neha and I will share the cost of the farewell cake.

Order of pronouns: “you” first, “I” last:

When pronouns and names come together, the order is second person, then third person, then first person. So “you” comes first, “Neha” next and “I” last. “I” is also the right subject form, and the sentence has no other error.

Why the Other Options are Incorrect?

Option 1: Either of these two lanes lead to the old fort near the lake. — Incorrect. The given sentence says “Either ... lead”. “Either” is a distributive pronoun and is always singular, so the verb must be singular.
Corrected: Either of these two lanes leads to the old fort near the lake.

Option 2: Kabir, who’s father runs a dhaba on the highway, brings us parathas. — Incorrect. “Who’s” means “who is” or “who has”. The word that shows belonging is “whose”.
Corrected: Kabir, whose father runs a dhaba on the highway, brings us parathas.

Option 4: The watch which Papa gave me last year it has stopped working. — Incorrect. The given sentence uses two subjects for the same watch. “The watch which Papa gave me last year” is already the subject, so the extra “it” must go.
Corrected: The watch which Papa gave me last year has stopped working.