My father is sick with cancer, he sometimes remembers, sometimes he can't ...?

You need to recognize the father as incompetent (limited legal capacity) and issue guardianship (guardianship) over him through the court. In this case, without the consent of the guardian (custodian), he will not be able to perform transactions.

According to Article 39 of the Civil Code of Ukraine, a natural person may be recognized by the court as incompetent if, due to a chronic, persistent mental disorder, he is unable to realize the meaning of his actions and (or) manage them.

Pursuant to Article 60 of the Civil Code of Ukraine, the court establishes guardianship over a natural person in the event of his/her incapacity and appoints a guardian at the request of the guardianship authority. The court establishes guardianship over a natural person in case of limitation of his civil legal capacity and appoints a guardian on the application of the body of guardianship and guardianship.

According to Articles 67 and 60 of the Civil Code of Ukraine, the guardian commits transactions on behalf and in the interests of the ward. The guardian gives his consent for the wards to perform transactions in accordance with Articles 32 and 37 of this Code.