How a 21 years old ask for parents to became legal in USA?

The son must file I-130 for the parents and then if the parents entered the US without inspection, the 601a waiver. Then apply at a US embassy...

There are no good options, there is no basis to immigrate or stay in the US because you have a minor USC child with needs. You can look into...

Expedited visa entry possible for child birth?

do you mean "greencard" e.g. immigrant visa? You can try, but prob difficult and if you try, I suggest you show you have health insurance...

Can I start working and then get the 'end date' typographical error corrected on OPT EAD?

Yes start working and don't bother getting this corrected, talk to the H1B attorney handling your case or/and if it was indeed issued incorrectly...

Will I loose my green card if I get divorced?

Absolutely not! Don't worry about this at all, plan on applying for US Citizenship in about two years. Best to you.

Changing employer. I-94 expiring Oct/04/2018. Current employer's I-797 expires 11/20

Find an employer to file the extension and change of employer petition before your current I-94 expires and asap. If this is very important to...

Filling the form to renew my is citizenship it asked where I applied the location, I don’t remember where?

You don't renew US Citizenship. If you mean form I-90 to renew your permanent residence card you can find the USCIS office where you were granted...

If you are a USCitizen, then marry and sponsor her for permanent residence. You can search the process on USCIS.gov, all the details are there. ...

Can I adjust my status from within the US?

Hello - you can adjust status in the US if you are in lawful status.

What is my next step? Is there something I'm missing?

You seem to have the basic documents. Once you file the DS260 you will get instructions on what else you need to file. If its a waiver case, you...