Family can see through disguises 100%. Anyone familiar with the person has a better chance. If the person is confirmed dead, I doubt you can claim what was inherited to his or her kids. NPCs would most likely see you as the risen dead lol. I need to fact check this but I believe once you are KO'd the disguise is broken and people can tell who you really are.
If you are 3 counties over you can pretend to be that person but once news travels(if it ever does) to your county you would be in trouble.
I'm planning on doing the same but being a detective. Once you create a disguise kit you can give it an alias. If you have different size heirs. I'm sure you could just recreate the kit and rename it the same thing. We are suppose to have a system in CoE where you can pass down items to heirs and have it become a family heirloom. Outside of that, we need to wait on more details.
It depends how you got the radish, did you pay for it and get it legally? If so, not really, as long as the farmer doesn't snitch. Or did you steal it? If you stole it and the farmer submitted a bounty for the radish then could be reclaimed. If you left enough clues where you stole the radish it is possible for you to be ID'd as the theft if you are caught before the convention.