A family law specialist prepared an opinion on the client's questions:
If the spouses obtained a divorce decree in Russia, there is no need to divorce again in Cyprus. If necessary, the decree can be registered in a Cypriot court, but this is not mandatory.
An agreement on dividing property and paying maintenance concluded in Russia has no legal force in Cyprus. If Dmitry stopped paying maintenance and Svetlana went to a Cypriot court, this document would not help her. For the agreement to work, it must be drawn up again and registered with a Cypriot court.
The couple's son Nikita keeps his citizenship after the divorce, because he remains a dependant of his father.
If Svetlana claims a share of the house, Dmitry also cannot rely on the Russian agreement in court. First he must have it legalised by a Cypriot court decision.
Svetlana will also keep her Cypriot passport. She obtained it lawfully and has not done anything that could be grounds for deprivation of citizenship.