I cannot find information about father’s family before they arrived in the US — from Wreschen, my ggf, Abraham I. JACOBS (b 1837; arr. 1855?), ggm Rachel SEIFFER (b. 1838); from Sawin, ggf Pinchus TRENCHER (b. 1851; arr. 1885?), ggm Leah Taube MARGULIES/GREENSPAN. Any help on how to proceed would be much appreciated.
Thanks,
Fran Jacobs

Fran,

Wreschen is known today as Września, Poland.
https://www.jewishgen.org/Communities/community.php?usbgn=-537153
Września, Poland
Alternate names: Września [Pol], Wreschen [Ger], Vreshne [Yid], Vřesno [Cz], Vzhes'nya

Sawin, Poland.
https://www.jewishgen.org/Communities/community.php?usbgn=-527389
Alternate names: Sawin [Pol], Savin [Yid, Rus]

Try searching https://www.jewishgen.org/databases/Poland/
for records of your family from those towns.  You can search by surname, or search by town alone to see what records are available.

Also, consider doing a soundex search on the surnames.  Names are often spelled in various ways.

Good luck in your search,

Sherri Bobish