There appear to be 4 main lines of de Franceschi's that are widely spoken of, dividing from Venice to 4 main regions of the Croatian mainland. However firstly in letters between Carlo de Franceschi and Kobler there appears there were an earlier 3 lines that were unrelated. Lets look at these first.
1 Domenico de Franceschi, it was not known from where he came. He married in 1614 to Lucia Grossich. They had 3 sons; Giovanni Paolo and Marco Antonio, who were municipal councilors in 1655 and are registered De Franceschi . The first married Margareta Vedova di Michele Andracca and had his son Giovanni Antonio, who was Doctor of Law and Municipal Chancellor. Francesca Piergiovanni and with her sons Giovanni and Marzio and daughter Margarita, who in 1697 married Ascanio Giacomini. The children then moved on elsewhere, I don't know where. - Are you perhaps a Descendant?
2. Valentino Defranceschi, who came from Carnia, was made Citizen in 1739, and with his wife Elena had 10 sons and 4 daughters, had a house in the Capuccini district and a vineyard in Plasè. He built, in 1764, the Chapel of S. Elena, he made a tomb for himself in the Cathedral with epigraph in 1785. Hi died in 1785. His son Ignazio had wife Giuseppa Danezello, was Civic Representative in 1783 and in 1785 at the age of 40 he died. - Where the others went , it does not appear
Giovanni Battista Defranceschi came from the County of Pazin around 1740. He was made a citizen in 1746, and with his wife Maria Maddalena had sons Giuseppe, Vincenzo and Giovanni. Giuseppe married Francesca Tomassich. Valentino, in 1793 married Orsola de Benzoni, and then had 4 children, one of whom, Francesco, retired Captain of Porto. He is now the only one in Rijeka. Giovanni married Catterina and a small house in Fiume, and was from Castellano di Bribir, where he died in 1807. I don't know anything about Vincenzo.
The Venetian De Franceschi's then leave and spread to Croatia, seemingly in 4 different directions. Notably Istra:
Istria is a historical region of Italy, but is today divided between Italy, Croatia and Slovenia. Towards the end of World War II the Istrian Italians were subjected to ethnic cleansing and genocide by the Yugoslavs, who occupied the land and annexed it to Communist Yugoslavia in 1947. About 350,000 Italians from Dalmatia, Istria and the surrounding region of Julian Venetia were forced into exile after the war. Their homes and property were confiscated and their cities were occupied by the Yugoslavs. The Istrian Italians and their exiled descendants patiently await the return of their homeland to Italy. (link to source)
1. Those of Istra's Ližnjan, Croatia, who have in more recent times moved to the USA and Germany
2. Those of Istra's Gologorica (Moncalvo di Pisino) and Gračišće (Gallignana) who later moved to areas such as Porec, Crikvenica and back to Gologorica. Later these families have migrated to USA, South Africa and Australia.
3. Those of Omiš and Imotski.
4. Those of Zadar, later migrating to Rijeka and Bakar