Don't try to hide the denial ... ask the attorney to put down the most recent receipt number.

Immigration ?

I agree with my colleagues, a sworn statement (affidavit) isn't 'enough'. Do you have school/medical records that show he was your custodial...

Can he file his EAD application (sure in US) on L2 visa, leave US and stay in his country till the EAD is issued? ?

I agree with my colleagues, yes on all counts.

What is the right date for change of statutes in form I539?

FIRST, people on E can study: https://www.ice.gov/doclib/sevis/pdf/Nonimmigrant%20Class%20Who%20Can%20Study.pdf SECOND, changing to F is NOT A...

Rejected B1/B2 visa once now applying for F2 visa

You say 'rejected' but I think you mean that the visa was denied. That denial will probably mean that the F-2 will also be denied ... with, or...

Can I stay while my I-539 is pending? ?

You can stay in the US while CIS is considering your request.

No, "you" can not file for a visa. BUT, she can file a form DS-160 ... go to the interview and provide proof that she'll be going back home for...

Immigration - Need a recommendation for an attorney who handles Fraud/Misrepresentation cases

Have you talked to the attorney that prepared the H papers?

How soon after spending 6 straight months in the US can a Canadian visit again?

My rule of thumb is "spend at least 1 day more back 'home' than you do in the US".

I had a misdemeanor 10 years ago, am I now legally able to travel to Canada with a passport ?

You need to tell us what specific misdemeanor you were convicted of.