@squishy2020 My apologies for my late reply. Things have been busy for me recently
My recommendations for feeding fiddlers that are too large for your octos is to kill the crab right before you offer it to Inky and use a stick to offer the dead crab to them. You can do this easily by inserting a wooden or plastic stake into the crab carapace at the back of the crab where the top and bottom of the carapace meet. I can post some photos of how I prepare my fiddlers for my octos if you would like.
I use a sharpened zip tie that's about a foot long and spear the crab with the end of the zip tie. Then I offer the crab to the octopus while it is attached to the feeding stick. The easiest way to trigger a feeding response is to gently touch the crab to the sucker cups on the octopus' arm. They have a lot of contact-dependent taste sensors on their sucker cups, so if you touch the prey item to their arm it will often trigger a feeding response. If you touch Inkys' arms with the crab and they push it away or run away from you, then remove the crab and try again in a few hours or the next day.
I agree with
@sedna that the crabs are a bit large for your animal, but if you kill them with the zip tie or wooden skewer before you offer them to Inky then you shouldn't need to worry about freezing the crabs and separating them into pieces. Inky likely won't be able to eat the entire crab, so make sure you remove the shell and remaining pieces of the crab shortly after they are done eating so that it doesn't harm your water quality.
If you have troubles with Inky grabbing the stick and not letting go, you can try to use the air-water interface (essentially the surface of the water in your tank) to encourage Inky to let go of the stick. This is done by slowly lifting the stick out of the water while the octo is holding on. They will likely let go of the stick and move so that their body remains in the water. If you are doing this, be careful to leave their mantle and gill openings under the surface of the water so that Inky can still breathe. You may not have troubles with Inky letting go of the feeding stick, but especially curious animals will grab onto the stick and not want to let go. Send a message if you are struggling with Inky letting go of the feeding stick and I can give additional recommendations.