1. Yoou should have lodged a police complaint for the said trespass against whoever had trespassed into your rooms,
2. Now it is too late to refer to earlier trespass,
3. Lodge a fresh trespass complaint showing it as a fresh treaspass and file a fres trespass case against the son of the tenant showing/stating that earlier illegal occupation was returned by them and this time it is fresh trespass,
4. Talk to your lawyer and chalk out a concrete and fullproof litigation plan to win the case.