Can we transfer H1B from company A to B when my dependents H4 Extension is in-progress with Company A is inprogress.

Yes, you can. The H-4 extension isn't really based on company A - it's based upon your spouse being married to someone who is maintaining valid H-1B status. As long as you are on a valid H-1B, there is no threat to the H-4 (may need to be proven with filing receipt for company B case, pay statements, etc.) You DON'T need to file another H-4 along with your change-of-employer petition for company B. The thing to watch out for is that the H-4 and your new company B H-1B will probably have different expiration dates - make sure everything is calendared so nobody falls out of status. Speak with an attorney for further guidance.

Your H1B status is employer specific. You can work only for an H1B employer that has properly filed an H1B petition for you, but there is no limit to the number of H1B petitions filed. You will maintain your status by being employed by at least one H1B employer at all times. However, your spouse's status is dependent upon your status. If you are maintaining your H1B status, then your spouse will maintain her H4 status, but she must be vigilant to extend her I-94 before expiration. Her application to extend her H4 status can be filed at the same time as your H1B petition through Co. B., but it is not required if her I-94 is not expiring soon.

The "query" should have been addressed with the employer's attorney, not strangers on . To answer your question, yes, you can change employer while H4 extension is pending. If the new employer's petition on your behalf is denied with you having left the previous employer upon filing of the new petition, the H4 will eventually be denied as well.