How long I can stay in the US on F-1 visa with an I-20 valid for one month?

You must discuss this with the school you wish to attend so they can admit you, issue a new I-20 and enroll you in SEVIS. This is also something...

Can I reschedule my green cad interview ? How much delay it causes to the entire process?

It is not a good idea to reschedule but if you must it can add anywhere from 2-10 months to the process in San Antonio.

Can a non-American born citizen use his American passport instead of his citizen certificate for the purpose of co-sponsoring?

The co sponsor's passport should be fine. Since you have an attorney you should be asking him/her. AVVO is really for people who do not have...

Will she be able to continue to work or have to take a break due to the change in the status?

There are a number of timing issues you need to consider, such as the expiration of the H-1 status (not the visa), when to marry, when work...

Can family come back into USA with valid visa stamp but revoked H1 and H4 petition and also pending H1 and H4 petitions?

First, you have an immigration attorney you should be asking. Second, AVVO is for people who do not have attorneys. Third, this type of specific...

You have an immigration attorney so you should be asking these questions of that attorney. If you prefer not to use your attorney for some reason...

It is assumed your AOS is based on a marriage petition, but regardless, if something goes wrong with the AOS then the F-1 might operate as an...

How long will it take for Green Card process - Family Fourth Preference for me , being from country Nepal?

Fourth preference traditionally and currently runs around ten years as the waiting period under the quota.

What should I expect next after I received form I-797C ? And Approximately when?

Assuming this was 2nd preference it probably should have been filed at all. But to answer your question those I-130s are taking 8-10 months.

H1 Selected, Changed Company, need to apply for F2 asap. Do you see any issues?

I see several issues and you need to see a qualified immigration attorney immediately.