Does the other party have the right to benefit from the apartment after each of them has moved to live in her own private apartment? And is the questioner sinful for not reconciling with them, even though they have not apologized to her for the bad talk, and she was neutral and did not initiate the quarrel?

Issues involving disputes should be referred to the Sharia judiciary. An old lease contract that lacks a specified duration for the tenancy is void, and the occupant of the apartment must return it to its owner; otherwise, they are sinful and an usurper. If the estrangement between relatives originates from their side, then you are absolved and bear no sin, and you are not obliged to accept an indirect general pardon. It is preferable to strive for reconciliation, as it is good, and the best of those who are estranged is he who initiates the greeting, and estrangement ceases with a mere greeting. Forgiving the wrongdoer is one of the best deeds and a path to attaining Allah's forgiveness and pardon.