Molesworth was twice married, firstly in 1825, to Harriet who was both the daughter of W. Mackinnon of Newton Park and the sister of the MP William Alexander Mackinnon and Lieutenant Colonel Daniel Mackinnon. They had six sons and three daughters, among whom were William Nassau Molesworth, engineer Sir Guilford Molesworth and solicitor John Molesworth (died 1886), great-great grandfather of Sophie, Duchess of Edinburgh. Harriet Molesworth died in 1850.
