Familysearch.org has some Valentinis in Venice. Take a look at the
indice below....Italy, Venezia, Venezia, ...on (Tribunale), 1871-1930 Venezia
Venezia Indici decennali (matrimo...rti) 1871-1881, 1882-1891
You have to take some time to search, but maybe you can locate something.
As far as getting info from Latisana on Family Search, I can't seem to get to the records to see if your name is there...
Italy, Udine, Civil Regis...ve), 1806-1815, 1871-1900 Udine Latisana
Matrimoni, indice 1815 (Registro 7694)
You can always email the comune and ask for civil records after 1865.
You would need to have some good dates, birth, marriage, death.
sindaco @ com-latisana.regione.fvg.it (no spaces in this email address)
So much more to advise, but maybe this will help you.