Extending stay in the US after H1B cap completion using FMLA leaves and applying the change of status to B2?

It is highly unlikely you can change status to visitor after staying in the US for at least six years if not longer.

Eb4 R1 worker?

Why in the world don’t you ask the attorney who is being paid to answer these questions?

Visas are only needed for travel. If you don’t need to travel their is no need to get a visa. What you and your must maintain is proper status....

Is it possible to apply for Re-Entry Permit?

Yes, you can probably get a reentry permit. And since you were admitted as a Lawful Permanent Resident the last time you entered there is no issue...

Can you be unemployed on an EAD?

You do not have to employed while having an EAD based on marriage/adjustment of status. Some others do have to be employed such as F-1 OPT, H-1,...

Conversion from H1B to H4 without spouse's H1b stamp?

An excellent question for the attorney being paid very well to represent you and your wife. Good luck!

H4 conversion without H1B stamping

These are excellent questions for the attorney being paid very good money to advise you and your wife.

Being on H1b, working form INDIA or long leave?

A great question for the attorney being paid to represent you. You should contact that attorney. The best option is your only option: use an H-1...

EB1C Priority Date

Yes you can retain the PD. But note that EB-1 manager cases require a large number of employees in the US. You must manage managers so that is...

That is not a problem. As long as the fees are paid it doesn't matter who pays them.