Have you contacted the police?
I would suggest that the first port of call be the police. Failing that, he needs to contact some solicitors ASAP.
It may be that an application for an injunction can be made but he will have to act quickly.
I hope this answers your questions. If so, kindly rate the answer and provide feedback.
If you have any further questions, please do not hesitate to ask.
The injunction would prevent any further action on the property.
Your relative would have to take action. No other family member could as they would not have had an interest in the property.
If the injunction is granted, the court will prevent any further dealings with the property until a further order is made.