You are generally correct about the process - PERM, I-140, I-485. You can track PERM processing times through the Department of Labor's iCERT web site: http://icert.doleta.gov/. Right now they report that they're processing PERMs filed on or around September 5, 2012 - so there's a roughly eight week processing time for the PERM.
With respect to the next step, a lot depends on how long it takes for the I-140 to be approved and what USCIS Service Center it will be filed with. Based on posted processing times, it will likely take about 4 months for the I-140 to be decided. Your husband may or may not be able to file the I-485 at the same time as his I-140 depending on what skill classification the I-140 is being filed under and what country he was born in. If he can file concurrently, then his I-485 will be submitted at the same time as his I-140.
Because you're married, you will be able to concurrently file an I-485 with his I-140/I-485 package as long as there's a visa number available for you based on your country of birth. The same would apply for your children. USCIS is taking a bit longer to process I-485s - about nine months.
Your L-2 status and EAD aren't really relevant factors in your husband's, and your adjustment of status beyond the fact that you were inspected and admitted into the United States and that by being in L2 status you've maintained lawful non-immigrant status while you've been in the US.
I agree with Mr. Isbell's answer.
PROFESSOR OF IMMIGRATION LAW for over 10 years -- This blog posting is offered for informational purposes only. It does not constitute an attorney-client relationship.
Up to a year for the PERM. Whether you can file the I-485 with the I-140 depends on whether your priority date is current. If it is not, you must wait for it to become current in order to file the I-485.
Your employer needs to retain an experienced immigration lawyer, whether myself or one of my colleagues, to review all the facts, advise them, and handle the case.
J Charles Ferrari Eng & Nishimura 213.622.2255 The statement above is general in nature and does not constitute legal advice, as not all the facts are known. You should retain an attorney to review all the facts specific to your case in order to receive advise specific to your case. The statement above does not create an attorney/client relationship. Answers on Avvo can only be general ones, as specific answers would require knowledge of all the facts. As such, they may or may not apply to the question.