"Below are some photos of the knives. I'm not sure what type of knives they are, nor how old they are. I purchased them second hand from someone who said they were purchased from a collector in Japan and being so cheap there was nothing to lose. One ferrule looks to be of brass, the other looks like some strange resin/plastic? The small one has a really thick spine also. Both have razor sharp edges, the sharpest I have in my collection. "
You have a Deba, a thick spined knife for breaking down fish. And a Yanagiba, a long thin blade for slicing fish from a fillet. They are both single bevel for right handed users. You can look up the words in bold on google and this forum.
Both knives appear several decades old, maybe 1960s. Your Sakai Ichimonji Mitsuhide Deba has a brass bolster which have not been used in Japan in quite some time. Your Sukeharu Yanagiba probably has a bolster made from horn. It looks too old for it to be a synthetic material.
The second photo looking down on the spines shows on the yanagiba some brownish spots in a line. Are those rust spots? Can't really tell without a good close up photo.