You will not find "Kafr Yasif" in Josephus because that is a modern place name.
In Josephus the supposed reference to this town occurs as part of the "divine dream" paragraph in the Life (xix, 27), and is as follows:
But wonderful it was, what a dream I saw that very night; for when I
had retired to my bed, so grieved and disturbed at the news that had
been written to me, it seemed that a certain person stood by me and
said," O Josephus! leave off to afflict thy soul; and put away all
fear. For what now grieves thee will render thee very considerable;
and in all respects most happy. For thou shall surmount not only these
difficulties, but many others with great success. However, be not cast
down; but remember that thou art to fight with the Romans." When I had
seen this dream I got up with an intention of going down to the plain.
Now when the whole multitude of Galileans, among whom were the women
and the children, saw me, they threw themselves down upon their faces;
and, with tears in their eyes, besought me, not to leave them exposed
lo their enemies; nor to go away and permit their country to be
injured by them. But when I did not comply with their entreaties, they
compelled me to take an oath, that I would stay with them. They also
cast abundance of reproaches upon the people of Jerusalem, that they
would not let their country enjoy peace.
When I heard this, and saw what sorrow the people were in, I was moved
to compassion to them, and thought it became me to undergo the most
manifest hazards for the sake of so great a multitude. So I let them
know I would stay with them. And when I had given order that five
thousand of them should come to me armed, and with provisions for
their maintenance, I sent the rest away to their own homes. And when
those five thousand were come, I took them, together with three
thousand of the soldiers that were with me before, and eighty
horsemen, and marched to the village of Chabolo ; situate in the
confines of Ptolemais ; and there kept my forces together, pretending
to get ready to fight with Placidus, who was to come with two cohorts
of footmen, and one troop of horsemen, and was sent thither by Cestius
Gallus, to burn those villages of Galilee that were near Ptolemais.
Where Chabolo is taken to mean Kafr Yasif, however, this may not be the case, because at the time there were a lot of villages in the area.
Personally, I would strongly doubt any definite biblical connections. First of all, Kafr Yasif, or "Kefr Yasif" as it was formerly known during the Mandate, was originally a very small village just southwest of Abu Sinan. This village originally had nothing in it, except the ruins of an old and small church. The entire area was heavily altered during the crusader period. Also, there are many larger, more ruined towns and tells all around, like Abu Sinan itself for starters. So, it is unlikely that Kafr Yasif has any significant antiquity.