Unfortunately there is no date on this one, but it appears to be a lock knife.
Blade markings: WHITBY MADE IN ITALY.
Two seaman's clasp knives with integral suspension rings and marlin spike. Marked 18th century, but I would guess early to mid 18th century.
Another suspension ring clasp knife marked 18th century. This one has a wood handle.
This one is of unknown origin. All metal. My guess would be another seaman's knife looking at the fish tail. Also of course a suspension ring type.