Re: immigration question
I believe with a green card she can sponsor her spouse and kids (only), which would take a few years. To sponsor anyone else you need to be a citizen, e.g. parents, siblings etc. To maintain a green card status you have to visit the US once a year/6mths (not 100%).
As for the kids, it would depend on how old they are. If they are under 18 its higher priority, if over 21 its different, and if married even more so.
Update: If you are planning to leave for more than 6 months (up to two years) you can apply for a Re-Entry Permit. If you are planning to leave for a much longer period, then you are at serious risk of losing your green card. Any travel abroad has to TEMPORARY in nature, and you must be able to prove continuing links to your life in the USA (mortgage, credit cards, family, etc.)
Disclaimer: I am a layman, not a lawyer. My opinions are not official or professional legal advice.