1. Since the matter is Sub-Judice in Court, the BMC will not act on the same based on the Architect's report. For removal or demolition of illegal & unauthorized portions, court order will be required.
2. Yes. You are entitled to file Police FIR, requesting investigation and charge-sheet, for offences like Trespassing, Cheating, Intimidation, Threatening, Fraud, Breach of Trust, Mischief etc.... (as the case maybe) against the person, supported with all relevant supporting Documents, Evidences & Witnesses.
3. IF the Police does not take action, THEN you can file private criminal case u/s 156(3) Cr.P.C., in the local Magistrates court, seeking directions to the Police to investigate and file charge sheet. The said Person may come down for settlement.