Tourist visa when green card being processed

[diat]

Hi Experts,

 

I am planning to start the green card process for my sibling, his tourist visa expires in 2018.

 

1. How much in advance can the US visitors visa be renewed?

2. If you have a valid visitors visa and in the interim apply for a green card can you visit the US while the visa is being processed?

3. Can you start an application for a tourist visa while the green card is being proicessed? Will impact the tourist visa decision?

 

 

Thank you!