This does not sound like a true "volunteer" position. The fact that you are not getting paid does not make it a volunteer position.

Validity of H4-visa stamping

Yes, if your wife were to leave the U.S. and re-enter using a valid H-4 visa, her status would then be H-4.

Visa for GC holder husband

Other than sponsoring your husband for a green card, there is no other status/visa that you can sponsor him for. If he does not want to wait for...

My L1 to H1b-15 conversion pending with USCIS.If I stay after my I-94, L1 Visa expiry, Will my stay consider as legal or illegal

You can remain in the U.S. while the Change of Status to H-1B is pending, but cannot work until the H-1B petition is approved.

Fiancé visa for GC holder

The K-1 is only for the fiancé of a U.S. citizen.

Can I continue with my H1B status after marriage?

You can, and should, maintain your underlying H-1B status, while also applying for permanent residence.

Proof of relationship for I-129F K-1 Visa

My suggestion is that the more information/documentation you present, the better.

Query regarding H1b Transfer

As long as you have an expired, valid H-1B visa in your passport, you can use it for any other H-1B employer during it's validity period. You need...

You can write a letter to the USCIS address on your receipt notice, requesting that the application be withdrawn.

I have multiple visa of U.S for 5 years, I am in U.S right now can I convert it into H1 employee visa what is the process thank

The first step is that you need an employer that is willing to sponsor you for an H-1B visa (assuming you are qualified - working in a position...