Dear Sir,

In case of joint audit under tax audit provisions... both of the chartered accountants need to sign on the report... however, if there is discrepancy in joint audit, they may opt for separate reports...

(Sorry Sir, i edited the earlier comment of disallowance, yes, the same is allowed and in such case, both of your CA's need to upload the tax audit report in the e-filing portal... and the procedure is same as done for one auditor... just add another CA in the list, after addition of 1st auditor..
sorry again for any incovenience caused).

Best Regards,
CA Lovely Arora
ca.lovelyarora @ gmail.com