Given the following context:

Until its acceptance by the National Trust, Belton House was always in the ownership of the family of its builder, though the failure of three generations to produce a son and heir caused the ownership to pass sideways and sometimes through the female line.
The owners of Belton are buried in the village of Belton's parish church close to the house. Their tombs are collectively one of the most complete sets of family memorials in England—continuous generation to generation for almost 350 years. The earliest Brownlow buried here is the founder of the family fortune the lawyer Richard Brownlow (1555–1638), and one of the most recent is the 6th Baron Brownlow (1899–1978).
The owners of Belton House have been:
Sir John Brownlow I (1594–1679) Bequeathed Belton to his great-nephew John Brownlow II.
Sir John Brownlow II (1659–1697). Builder of Belton House
Sir William Brownlow (1665–1702). Brother of Sir John Brownlow II, permitted his widowed sister-in-law Alice to retain Belton.
Sir John Brownlow III (1690–1754). Created Viscount Tyrconnel in 1718. Nephew and son-in-law of Sir John Brownlow II.
Sir John Cust, 3rd Baronet (1718–1770). Speaker of the House of Commons and nephew of Tyrconnel.
Sir Brownlow Cust (1744–1807). Created Baron Brownlow in 1776. Son of Sir John Cust.
John, 2nd Baron Brownlow (1779–1853). Created 1st Earl Brownlow in 1815. Son of Sir Brownlow Cust.
John Egerton-Cust, 2nd Earl Brownlow (1842–1867) Grandson of John, 2nd Baron Brownlow.
Adelbert, 3rd (and last) Earl Brownlow (1844–1921). Brother of John, 2nd Earl Brownlow.
Adelbert Salusbury Cockayne Cust, 5th Baron Brownlow (1867–1927). Second cousin of Adelbert, 3rd Earl Brownlow.
Peregrine Cust, 6th Baron Brownlow (1899–1978). Son of the 5th Baron Brownlow.
Edward Cust, 7th Baron Brownlow (born 1936). Son of the 6th Baron Brownlow.
The National Trust (1984 onwards).

answer the following question:

What was the name of the family that owned Belton House before it was accepted by the National Trust? 

Brownlow