Complex sentence: The family sold the castle in 1738, and it remained in private hands until Colonel James Barclay Milne, whose grandfather James W. Barclay bought the castle in 1901, placed it in state care in 1946.
Split into simpler sentences: The family sold the castle in 1738, and it remained in private hands until the 20th century. James William Barclay bought the castle in 1901, and Colonel James Barclay Milne, his grandson, placed it in state care in 1946.