Do I need to leave the country to apply for an EB1?

Probably not if the O1 is valid when you file I-140 and I485 contemporaneously.

Please advice if there is any need to send letter to USCIS to with withdraw pending H4 extension or not.

It is up to you. If you want everything to be in order, it is a good idea to notify USCIS.

1)Do I need to apply for new H4 or can she travel on existing H4 stamping ??. /

If your spouse's H1B is valid you can use your existing H4 during the period of its validity.

Does my son have to present at the time of interview?

I agree with Alexander. Your son has his own benefit under adjudication and needs to be present at the interview unless such presence was waived.

When was my grace period started, my sevis was in completed status as of Feb 2nd. what options I was left with.

The grace period is 15 days if the program whether course of study or the OPT was not completed and 60 if it was.

Can we change our status from B1 B2 visa to permanent residency??

There is no direct method to adjust your status from B1/B2 to permanent resident. You may be able to change your status from B1/B2 to a...

How can she come with her kids once my petition is approved

You could petition for your mother to receive an immigrant visa if you are a United States citizen. You could also petition for your siblings if...

You are authorized to be in the United States while seeking asylum but you are not in a valid nonimmigrant status. You could not seek adjustment of...

Could getting married to a US citizen allow me to become a permanent resident again?

The answer will honestly depend upon more information about your drug possession conviction. You may be able to obtain lawful permanent residence...

Do I need to file an separate I-130 for my daughter?

You do not need to file a separate Form I-130 for your daughter unless you intend to naturalize while your family members wait for their immigrant...