My H4 EAD start date is prior to my H4 start date. Is my H1 still valid?

You need to check with your immigration attorney to see what was requested on the forms. Doesn't he/she know the answers to your questions?

If my husband came to the US in a B12 visa and the exceeded his time of stay. Would he have to apply for I485 ?

Based on this information, he can file an I-485 with no waivers, assuming you also file an I-130 petition and all of the evidence required for that.

Divorce?

This is a family law issue, not immigration. Good luck.

My younger sister is in Pakistan she wanted to come to US to pass an examination and to attend the seminar?

So, you are asking a group of lawyers if your sister should lie on her visa application and commit visa fraud. Really?

I129F Biometric Appointment?

No, the petitioner does not get a notice requesting biometrics be given.

Can my step brother who is on h1b can sign affidavit of support for f1 visa ?

Anyone can sign the I-134 affidavit of support. They also need to show their source of income/savings.

My employer was applied EB3 H1B initially and later converted EB2, now EB3 is filling is current date, Can I apply 485 on EB3 ?

Yes, you can as long as you and the company intend for you to work in the EB-3 position. Doesn't your immigration attorney know this?

Your question is contradictory since you don't need a change of status if you are leaving the US.

Is there anyway to start working before the start day on your EAD card?

The only way you can get H-1 status by then is if it is a cap-exempt employer. If it is not cap-exempt, even if you are selected in the H-1...

H1B?

The H-1 petition may remain valid but you will be out of status once you stop work.