Here is my update after a recent travel out of the country and back to the U.S.
Our port of entry was Los Angeles Airport.
We travelled in a group of four; me and my wife with green card and parents with the B1/B2 visa.
The CBP officer directed us to complete the immigration process together. We even filed only one customs declaration form.
CBP prefers to process families together. As green card holders, you can choose the line for permanent residents. Bring your parents with you.
Credit:stackoverflow.com‘