This rumour had mentioned that Mahinda Rajapaksa's wife Shiranthi Rajapaksa (née Wickremasinghe) is the daughter of the elder brother of Ranil Wickremesinghe's father. An external fact checker has confirmed that this is false after an investigation. Read more here (Sinhala with some family charts in English): https://srilanka.factcrescendo.com/2021/08/11/clarity-on-ranil-wickremasinghe-mahinda-rajapkasa-blood-relation-claims/.