Necessary party in civil suit

Sir / Madam, The defendant entered into agreement to sell the suit property during pendency of suit. Before sale deed could be executed the concerned fact brought before the court and ad interim relief order passed prohibiting execution of further document & transfer of possession to third party. Even during the ad interim order possession is given to third party by defendant though sale deed is not registered and ownership or right to possession is not transferred to third party. 1. Whether third party is necessarily required to be added to suit even though ownership is still with defendant? 2. Whether third party is necessary party for proceeding under order 39 rule 2a of CPC ? 3. Can we pray to hon. Court under 39 rule 2a to evict third party from suit property and seal the property? Any case law in this respect will be very helpful. I will be grateful to you. Thank you.