H1B - Can i Change Employer just days before my I-94 ends?

These are not questions for this general forum. Further, the correct party to ask is the immigration attorney for company B presumably preparing...

How do i know if i am a us citizens

it is not automatic. She must apply for you. Seek experienced immigration counsel to help.

Does L2 Visa with Valid L2 EAD till April 2020 need to apply for new EAD on Feb 2018, If the new L2 applied?

You should be fine as long as his L visa is extended since your L2 is dependent upon his L1.

File the I-765 with her own I-485.

Check with your DSO if your SEVIS should be re-instated. Meanwhile, pursue your GC-EAD based upon marriage.

How long does H4 to F1 COS take?

Once the I-20 is issued, your son can get his F-1 from your local Embassy in your home country by making an appointment. So I do not know why you...

How soon can I submit my I-485 after my USC spouse filed I-130 as standalone last week, July 2018? I’m F1 overstay, married 2017

The I-485 could have been filed concurrently with the I-130. File it now.

Mention it if it fits exactly in the 9 digit space provided.

Tickets 30 yrs old. paid in full?

This is not an immigration question. You need to ask a criminal defense lawyer who deals with traffic infractions.

Can I leave the USA without getting my green card in the mail for immigration visa?

Wait for your green card. Otherwise, make appointment with local USCIS office by going to www.uscis.gov for infopass appointment and ask for I-551...