You can buy those one sided razor blades at most hardware stores as well. Painters use them also to scrape paint off glass. You can also use those scripto knives that artists and hobby/craft folks use. They are virtually the same as a scalpel...
Castrating a more mature ram lamb at that age and size by yourself is very problematic at best as you will have a high risk of bleeding out the animal from cut blood vessels or if they survive a high risk of infection and a huge Vet bill or death. You would need a burdizo clamp to crush the blood vessels and surrounding tissues then cut them off below the crush area then hope that the crushed tissue holds. Surgery is the same as for horses and other more mature animals. Best bet for these ram lambs is to castrate them at just below the head and invite them to a BBQ. Write it off as lesson learned and castrate the ram lambs as soon after birth as possible.
I used to raise meat goats & did a LOT of banding. They were obviously going for meat so not a real issue with the crystals, etc. At about 3-4 days I would go in and band them. BE SURE you have both testes down & don't catch the nipples. Fast, easy (if you feel for 2 balls) and after a huge scream, they ran to mom and nursed. Then they would lay down, within a few minutes all got numb. No more problems. There was NO smell, NO rot, etc. About 10 days later they had just shriveled and fell off. Really guys, they are smaller than a quarter skin and all.
I have a burdizzio and use it for an older (2-6 mos) but, that is much harder, louder, far more annoying (for all of us) and I just don't feel badly about banding....or the clamp, if done early. The ONLY reason for waiting longer than a week is if you are keeping the wether as a pet...then there is evidence that the early castration can limit the size of the uretha and may be more conducive to crystals.
Pigs, ya can't clamp, gotta cut & pull those rascals out. Talk about squealing and biting!!!! (OK, if it were me, I'd do the same! ) Horses & cattle, ya need a good vet.