How do Rama and Sita influence Hindu marriages?
They influence Hindu marriage system. They influence people not to have second marriage. This is the reason why divorce are less in India.
Its Hindu Sita (also spelled Seeta or Seetha) (Sanskrit: सीता, "Sītā", listen: Sita (help·info) meaning "furrow") is the wife of Rama, the seventh Avatar of Vishnu in the Hindu tradition. Sita is one of the principal characters in the Ramayana, a Hindu epic named after her husband Rama. She is esteemed as a standard-setter for wifely and womanly virtues for all Hindu women. Understood theologically in Hinduism, Sita is an Avatar of Lakshmi
Ramayana is considered to be an historic event. Rama was banished from his place by his father. This Father was forced to ask Rama to take exile for 14 years to please his third wife Kaikeyee's wish. Sita the wife of Rama promptly followed Rama. The Rama's brother Lakshmana also joins Rama and Sita.
No, Sita was a foundling, discovered in a furrow in a ploughed field, and for that reason is regarded as a daughter of Bhudevi, the Goddess Mother Earth. Sita is the wife of Rama, the seventh avatāra of Vishnu in the Hindu tradition and is esteemed as the standard setter for wifely and womanly virtues for all Hindu women.