The use of the word 'either' and 'whether'

Seorang teman bertanya tentang beda penggunaan kata 'either' dan 'whether' dalam bahasa Inggris.

Maka berikut ini adalah jawaban yang saya berikan berdasarkan pemahaman dan pengetahuan yang saya terima selama ini.

As far as I know, the use of either is different from whether.

The word 'either' is used when you have two or more options both in negative and positive forms e.g.:
- Either going to Surabaya or visiting her grandmother doesn't make any different because her grandmother lives in Surabaya too
(Entah/Apa pergi ke Surabaya atau mengunjungi neneknya tak ada bedanya sebab neneknya tinggal di Surabaya)

- You don't have any choice in this situation, either surrender yourself or you go to prison. Both are the safest way to solve your problem
(Anda tak punya pilihan dalam situasi ini, entah/apakah menyerahkan diri atau anda masuk penjara. Keduanya adalah jalan teraman untuk mengatasi masalah anda)

- We should do trial conference call either by skype or yahoo messenger before invite a bigger number of people there
(Kita sebaiknya mencoba conference call entah/apa menggunakan skype atau yahoo messenger sebelum mengundang lebih banyak orang kesana)

The word 'whether' is used in indirect sentence for interogative question (yes-no answer) e.g.:

- Do you want some milk? (Direct sentence for interrogative)
The indirect sentence will be:
I asked them whether they wanted some milk.
( Saya bertanya pada mereka apakah mereka mau susu)

- are you ready to go?
The indirect sentence will be She asked her friend (man) whether he was ready to go.
(Dia bertanya pada temannya (pria) apa dia siap pergi)

Please note that the word 'whether' can be replaced by the word 'if' that has the same meaning. So the above example can also be stated:
- I asked them if they wanted some milk.
- She asked her friend (man) if he was ready to go.