Just a quick review by posting those census records again.
1851 census Mitchell Street Beithhttps://www.freecen.org.uk/search_records/590279c6e9379091b11826b2/robert-love-1851-ayrshire-ayr-1842-?locale=en1861 census Mitchell Street BeithJohn LOVE 58 head born Beith, cotton weaver
Margaret LOVE 56 wife born Dalry, silk sewer
Robert LOVE 18 son born Beith, cotton weaver
Andrew LOVE 15 son born Beith, cotton weaver
John LOVE 12 son born Beith, print tarer
William LOVE 9 son born Beith
From your original post, we are s
till missing information on the sons Andrew and Robert. Neither are found in Scotland after 1861.
Andrew is the only son NOT named on the Beith memorial inscription mentioned in the opening post, so I wonder if he emigrated. I think you might need to look abroad for him.
According to the memorial inscription, Robert was aged 26 when he died. But nothing has been found for him around 1868-70. I have to wonder if there is an error in the transcription of that memorial, and Roberts age at death has been mis-recorded, or there is some other error. It is quite a coincidence that two sons died at exactly the same age. Has the original memorial been sighted?
There is a
Robert LOVE born abt 1842 Beith Scotland who appears in the English census from 1881 to 1911 living in St Albans Hertfordshire, occupation draper. His wife is Janet Rodger BARBOUR and they married in 1871 West Derby. He has quite a few children with names that follow the family names for the LOVE family including daughters Agnes Kerr LOVE born 1875, Margaret Kerr LOVE born 1876. I suspect this is your Robert.
If so, then Robert married his cousin. Janet was the daughter of Agnes KERR, sister to Margaret KERR.
Agnes married Peter BARBOUR and the family moved to England between the 1861 and 1871 census.
1901 census:
https://www.familysearch.org/ark:/61903/1:1:XS4D-XM81911 census:
https://www.familysearch.org/ark:/61903/1:1:X7LQ-3P5