Payment dispute among the inventors

A  service for patent was requested to  a law firm by three inventors. Dr Rajesh, Dr Nehru, Suresh.  Suresh being the student of Dr Rajesh and Dr Nehru. The invoice was generated in the name of Dr Rajesh,  Dr Rajesh paid the money to the law firm at various stages during the patenting process.  After 16 years patent got granted. Now some Payment is due. Dr Rajesh and Dr Nehru both are pressurizing the previous Student Suresh to clear the dues claiming that Suresh has never paid any amount. But even Dr Nehru has never paid anything. (Dr Nehru lives in Canada). Actually, the patent is the result of research work conducted by Suresh under the supervision of Dr Rajesh and Dr Nehru during Suresh's PhD. The invoice is still coming in the name of Dr Rajesh.  Dr Nehru has also never paid a single amount. But now both Dr Rajesh and Dr Nehru are pressurizing Suresh to pay money to the law firm.  They are keeping the lawyers in CC in those emails in which they are demanding the payment. It has become a source of tension and harassment for Suresh.    Dr Nehru  is an Indian,  living in Canada, Suresh and Dr Rajesh both are living India. My question is : 1- Can the invoice be now changed by the law firm in the name of Suresh after getting influenced by Dr Rajesh and Dr Nehru? 2- What would generally a law firm do in such cases? To whom they will catch for the payment?Dr Rajesh on whose name the account was opened or Suresh or Dr Nehru or all?  Will they settle for 1/3rd payment for each one? Note:  All three have provided power of attorney.   Suresh is the first inventor and applicant in the patent application that the law firm filed in the patent office.  The service from the law firm  was requested by Dr Rajesh  and so the invoice was always generated in the name of him.