I think the key source for the Melville of Raith family is a book: The Melvilles of Melville and Leslies of Leven: Vol. 1 (of 3), Memoirs, by Sir William Fraser, publ. 1890: a PDF is available at http://www.tannerritchie.comhttp://www.tannerritchie.com [for purchase]. Volumes 2 and 3 are freely downloadable, but less useful. Page 445 ff. of Vol 1 has a “complete” family tree of the Melvilles of Melville and their subset the Melvilles of Raith, well into the 18th century. Unfortunately neither Richard Melville nor his son Andrew Melville is identified there.
What is the source of your “strong suggestion” that there is a relationship between the families?