1. It is a prosecutable offence of mischief, cheating, breach of trust etc.... to conduct Registration of Same Property, while the earlier registration transaction is in force. In law, nothing is done automatically and proper & due procedures of law has to be followed at every step.
2. Since Dr. Phani is the First tenant (who could claim losses), ONLY & ONLY Dr. Phani can file the above complaint and NOT Dr. Suresh. Here again Dr. Phani cannot file because he himself is the witness in the Tenancy Agreement with Father & Dr. Suresh.
3. Here Dr. Suresh is guilty of Trespassing, since he knew that premises is rented to Dr. Phani and that he cannot rent it from your Father. Hence by virtue of this, NOW he cannot claim anything or file any claims in any court, except to harass you.
4. Get a POA from father and you can Serve a Proper Legal Notice to Dr. Suresh to vacate the premises, on the above grounds, else you will file police complaint against him.
5. You can also file a complaint against Dr. Suresh, with the state Medical Council /Association, for such harassment, intimidation and malpractices.