I have found a Lot Roberts b. 1850 in Reynoldston, Pembrokeshire (Farmer) on the 1891 and 1901 Census.
Could he be yours?
Living with Martha (wife) b. 1850, Amroth
William, 1874 - Marros (Carmarthenshire)
Margaret, 1877 - Marros "
Rosanna, 1879 - Marros "
Martha, 1881 - Marros "
Joseph, 1883- Marros "
James, 1885- Marros "
David John, 1887 - Cyffic "
Thomas, 1889 - Cyffic "
Mary Roberts (mother) b. 1812 in Begelly, Pembrokshire