1. If one's parents are green card holders and are residing in the US, then if they wish to sponsor their son who also is already residing in the US on another visa, how long does that typically take, compared to if he is outside the country, and

2. How often does one need to visit the US to maintain validity of the Green Card ? (Is it still once a year ?)

Passport Application Questions:

Immigration application outside country of origin?
Association of Immigration Consultants?
Immigration Forms - Does anybody know any good secure/safe website , which offers cheap form filing
Immigration Interview - Now I have recieved visa Interview call
Dual Immigration Status in USA and Canada?
Taking Immigration Photo
Immigration Pictures
Where to start with immigration process?
Canadian immigration processing times?
My wife and I are US citizens sponsoring her daughter's husband's immigration process
Immigration Visa application at Consulate?
Green Card renewal/Citizenship?
Interview for Green Card: Questions + Advice Needed
Lost Passport
AOS and renewing passport?
New Green Card Question-PLEASE?
Renewal of green card?
Renew green card or get citizenship
Renewing Green Card
Renewing Passport
new green card holder out of US for the first time?
Renew Passport - My passport will expire in January
Renew Us Passport I have recently got US passport.
Replace Green Card lost my wallet which contained my Permanent Residency Card
Immigration requirements on moving family to England?
Minimum education requirements for Green Card?
Green card interview - how do relatives visa status effect green card issuance?
U.S. Passport Application Form Question
USA Green Card Lottery,Why You Do Not Win?
Canadian citizen visiting USA passport question?