Differences in agreements between partners leading to liti

Hi Everyone! During a partner retirement from the firm we made 3 Agreements. 1) Retirement Deed mentioning he is entitled to receive only15 Lakhs from the firm. Even in his Capital Accounts it was signed by himself as 15 Lakhs as his Investment. This deed presented before District register after 2 months & his Retirement is done. This agreement & Letterhead Agreement were made 1 month prior to unregistered agreement No. 2. 2) Unregistered agreement on 100 rs Stamp paper saying that he received 15 Lakhs & also extra 5 lakhs for a total amount of 20 lakhs was received from firm & also one Flat X which will be registered to him which the firm got out ot 8 flats through development agreement with landlord or to a 3rd party person on his behalf in a mutually understanding agreement. 3) On a firm letterhead, a separate agreement was made saying that Market value of flat x which we offered him was decided at 90 lakhs & the sale deed amount (white amount ) which is 40 lakhs should come into the firm Account either if it is registered to him or to 3rd party on his behalf & the remaining amount i. e., 50 lakhs above or below should only be taken by the retired partner. Thus, things remained at this situation. Recently the partner sent a legal notice saying that flat should be registered without sale deed amount of 40 lakhs to him or to a 3rd party on his behalf. He is completely violating the agreement made on the Letterhead. My question is how can we register the flat to him while in the original retirement deed its only mentioned that he should only receive 15 Lakhs from the firm & how Can we register to him or Especially to some 3rd Party on his Behalf without Sale deed amount of 40 Lakhs reflecting in to the Firm Account who is no where related to Firm business ? Please help. Thank You!!!