The employer would need to file a petition to extend the H1b, and you could get the new visa abroad.

Can I easily come on a tourist visa for 6 weeks for vacation and job interviews in my case?

You should be worried about coming to the U.S. for job interviews more than anything.

Dual/ Nationality Canada /USA trip

Most likely the Canadian authorities will require you to provide your Canadian passport. But that is up to them.

I am filing for Advance Parole as part of an Adjustment of status application. Do I need to submit explanation on why I need AP?

Yes, you need a reason, and yes what you suggested is a valid reason.

I am a J2 visa holder subject to 2 year home requirement. what happens if I get my I-140 approved but cannot get a waiver?

You can apply for a waiver separately from your husband, you can continue on a J visa, and you can leave the U.S. and process for the visa abroad...

My asylum confusion!

Yes the EAD remains valid.

How do i find out if someone is on a passport denial list

You could try calling the passport agency.

USCIS "Policy Memorandum" dated Nov. 15, 2013 "parole in place" for Military Families, Can i be eligible (sibling) ?

It is extremely unlikely that you can be granted parole in place. You can request deferred action status.

Can i enter the USA on B1/B2 to.....

It is very risky, but not technically in violation of the visa.

What type of visa would we apply for?

She can apply for a tourist visa. If you are a U.S. citizen, you may be able to file an immigrant visa for her.