1) you should move court and seek injunction restraining B from selling the plot . make your son , B and purchaser X parties to the suit
2) you can have papers circulated for urgent reliefs after issue of notice to defendants
3) court would grant order for maintenance of staus quo and direct defendants to file reply
4) defendants would fie reply to interim application and after arguments court would grant you stay pending hearing and final disposal of suit
5) In the case of Dipakbhai Manilal Patel (supra), Court has held and observed in paragraph No. 4 to 6 reads as under:-
(4). Whenever, the Suit pertaining to immovable property is filed, the provisions of Section 52 of the Transfer of Properties Act are applicable on the principles of lis pendens in normal circumstances. you can the notice of pend ency of Suit
5) The essential purpose of registration is to see that any person who may be interested to purchase the property when undertakes the title search of the property with the sub- registrar, the person concerned would be put to notice that a particular suit is pending before the competent Court and therefore, he may not be misguided or if with conscious knowledge, the person concerned has purchased the property, the purchaser may not be in a position to contend that he was not aware about the pendency of the litigation