Do I need a lawyer by law?

There is not a legal requirement that you use an attorney for green card processing.

How many months does a green card holder have to stay in the US out of the year in order to maintain status? Any recent change?

Six months is still the rule, but your plan to do six and six could be problematic if that is the forever plan. If it is short term, you may want...

Where do I send my form 1-134 to?

You send it and all supporting evidence to your relative to be included in his visa application or to bring with him to the interview.

How can i file for my step brother, we are from the same mother, but not the same father?

A U.S. citizen may, by law, petition to have brothers and sisters (siblings) immigrate to the United States in certain circumstances. The...

What is the effect of my pending divorce and plan to re-marry, to my pending F2B petition to my son ?

You are permitted to file on behalf of your son regardless of your marital status.

Conviction of any criminal offense may make one ineligible for the SENTRI program.

What my answer should be

Answer yes and then in your cover letter where you state what supporting evidence you are sending with the application include a reference to a...

How can I get him back in to the country for his kids and I

It is probable that he has a lifetime ban. You should visit with an immigration attorney and review his criminal history and immigration violations...

Immigration

You can conclude that they received your application and you have paid the fees.

What I need to do to bring my cousin to the United States

There is not much you can do, but he can file for a visitor's visa.