Difficult GC situation..any help is appreciated

[geetikakhare]

My parents got there green card in Sept 2001 as my Mother's brother sponsored her in 1987 for the same. They visited USA four times for periods of 2-3 months between 2001 and 2004 march. In march they applied for two year stay, I think its called re-entry permit...and then stayed in India for two years and visited again in 2006 March. They are practicing doctors in india and they find it hard to visit every 6-8 months to US in order to maintain their Green Card. At the same time we wnat them to be able to immigrate after next couple of years as both their daughters are in USA. ` We are trying to see if there is a solution to this. Here are some of our concerns & questions:
1. It will be 5 years in Sept since they got their Green card. Are they eligible for citizenship? Will it help if they stayed one year untill next March and then file for citizenship, will they get it?
2. Can they apply for another two year stay if they can not be citizens now?
3. If they surrender their Green card, will they easily get a visitor's visa?
4. My sister is also got her employment based green card two years back. Once she files for citizenship after 3 more years, how long will it take for her to get citizenship? After that can she file for my parents green card again, incase they surrender theo=re GC now and take a visitor's visa? If yes, How long does it take if a married daughter files for her parents?

[kk]

1. No. They have to be physicall staying in the US most of the times. Read https://www.immihelp.com/us-naturalization-eligibility/

2. They can. But read https://www.immihelp.com/retain-greencard-useful-tips/

3. Really depends. Hard to tell.

4.
A. Eligibility: https://www.immihelp.com/us-naturalization-eligibility/
B. Yes, she can.
C. Read http://www.immihelp.com/greencard/visa-bulletin.jsp