I know how to remove the pits from stone fruit. I want to remove the seeds from the pits. Every attempt I keep damaging the seeds. Trying pliers or a knife i could get hurt. is there a safer way to get the seeds out? .
It's a nut, nutcrackers work. Assuming you don't have and don't want to buy a suitably large and controllable nutcracker, (the long-lever type would be suitable) the next best option is probably compound leverage locking pliers - UK Mole Grips® or USA Vise Grips® or their copy-cats.
Because of the way they operate, the jaws can be set to not close all the way, so they can be set larger than the kernel is wide, and then used to crack the shell with no risk of pinching you, and less risk of damaging the kernel. Set the pit in the jaws so the seam is touching the jaws (you want to allow it to pop open, not crush the shell in a way that holds the seam closed and requires brute force and fragmentation to break the shell.)
As it happens I have some peach pits I was simply going to plant, but some sources do suggest cracking the pit off first, so I'll make some pictures:
You could also attempt to use a C-clamp, but that's likely to be frustrating as it's hard to keep a nut in the clamp.
If you leave the stones out to dry out for 24-48 hours or so, if you use a blunt knife (e.g. butter knife) you should be able to split the pits without too much effort. If you have a bradawl you can start spitting the husk with that. The outside needs to be completely dry though.
As others have suggested you could also try nutcracker pliers when the pits are dry but you run the risk of crushing the seed inside.
(I successfully used the butter knife technique with peach stones in an attempt to grow a tree).