Given they are adjacent family units, a reasonable conclusion is that "over spill" from the
congested parents home to the less congested grand parent's home, however someone may know better :-)

1851 Lydney

29
BATH William 42 Dealer in Iron Works Lydney
Mary 37 Elloe Gloucestershire ?
Edwin 12 Lydney
John 10 Lydney
James 5 Lydney
Elizabeth 6 Visitor St. Briavels
William son 10m Forest of Dean
JONES Visitor 12 Yorkley
BLUNT George Lodger 18 Staffs
30
PARKER Elizabeth Widow/er 69 Lydney
James 43 Labourer Lydney
BATH Benjamin Grandson 10 Scholar Lydney
Thomas Grandson 6 Scholar Lydney
Henry 4 Grandson Lydney
PARKER Martha Grand Daughter 2 Lydney