Me again - assume you have the census records:
In 1871 at 12 Jutland st, you have:
Andrew Landrum head 56 m b Ireland
Jane Landrum wife 55 m b Ireland
Jane Stephens dau 26 u b Ireland
Thomas Landrum son 19 u b Ireland
Andrew Landrum son 15 u b Preston
...so this would be your Andrew aged 15.
Given that Thomas was born in Ireland and Andrew in Preston, we can assume they came over between 1852 and 1856 approx although I can find no trace in 1861 census
Then in 1881 45 Gillett Street, Preston
James Swindlehurst head 28 m b Preston, Lancs
Jane Swindlehurst wife 35 m b Ireland
Andrew Landrum father in law 68 w b Ireland
Sarah Landrum sister in law 28 m b Preston
Ada Landrum dau (of Sarah I assume) b Preston
Jane Stephens has remarried to James Swindlehurst
Sarah is married to Thomas Landrum (see above 1871) - she and Ada appear twice in 1881 census, here with the Swindlehursts and also at home with Thomas and other children in Accrington....
I have also census records for your Andrew and his family from 1881 onward if you don't have them?
There are census records for Alexander and Mary Ann in Preston from 1861 through to 1901. Interestingly in 1861 they have a visitor - John Stephens, a 17yr old carpenter from Ireland - wondering if some link to Jane Stephens above?
In 1861 the only other Landrums in Preston seem to be George (62yrs), his wife Kate (52 yrs) and their children: William (21), Andrew (18), Jane (16), Mary (14), Margaret (12), with lodgers Mariah Nixon (17) and Ellen Stephens (14) - Stephens again...can't be just co-incidence...although I can't work out how George and Kate fit in with my Alexander or your Andrew...
So frustrating as I'm sure the link is there, just got to find it...
Suitcase