Can H4 Visa holder do intra-trading in US?

You are not supposed to work. Period.

I will be on OPT from sept'12. I m having a job offer. How long can I stay back in home country without violating F1 visa status

If you return while you still have a valid visa you should be ok I think.

Should be fine.

Can i get a waiver?

Where are you? Are you in the us?

How to obtain a green card again?

The same way you did before. An I -13o petition.

Change of visa status from L2 EAD to H1B

Yes she can have a new h from the L before oct 1. You cannot switch between Ead and h. You have to pick one.

What forms are needed for my B1 status husband to change to immigrant status?

I agree with attorney Amos.

I am planning to change my status from b2 to F1...Kindly let me know if its going to work

Student visas are specific. Things you mentioned are not as important as what you want to go to school and why are you going to school now here.

Does differed action apply to children who came legally on tourist visa but are currently out of status?

We believe entry does not matter. But once the final rules come out we eill know for sure.

My OPT will expire on Feb 2013, I am working for a sofware company. Is there any way that they can file for H-1B before my Opt

Not with your current employer. You could try for cap-exempt employment.