Thank you for the information.
1)
Do I have to post to the address written in AR-11 form which is
US Dept of Homeland Security
Bureau of Citizenship and Immigration Services
Change of Address
PO BOX 7134
London, KY 40742-7134
OR
to the vermont service center.
-- Send the AR-11 form to the London, KY address. Post the generic letter (step 3) along with the copy of the AR-11 to Vermont Service Center.
2) Do I have to send the AR-11 letters of my spouse separately? or can send it together in one mail?
-- Seperate AR-11 forms for you and your spouse. You may send them in one cover to London, KY. For VSC, one letter should do for both of you. keep copies of I-485 receipts also for VSC.
Thanks
Vinish