Under Partnership Act, every partner is bound to carry on the business of the firm to the greatest common advantage, to be just and faithful to each other. What the partner is doing is fraud and is bound to indemnify the firm for the loss caused by fraud. Any partner making personal profit out to business of firm is bound to account for it. If it is feasible you can throw the fraudster partner out and recover any loss suffered due to his fraud. You have already issued notice to landlord to vacate the premised by 21 March 2021 and thereby terminated the lease agreement. You can continue in the leased premises but then the rent will not be the agreed rent, the landlord can impose his rent as long as you stay in the premises. You certainly have a case against the said partner. You can proceed against him in criminal Court for cheating under Section 420 and collect the loss due to fraud by the partner. You can also file civil case for recovery of loss under Section 10 of Partnership Act.
For resolution of dispute among partners, the firm need not be registered under Partnership Act. You can take all the measures against the partner available to a registered FIR.