Is it safe to use some one's used tapers and jewelry if it is properly sterilized?

Well. You’re asking “if it is properly sterilized.” Anything is reusable if properly sterilized. But I wouldn’t apply that to heroine needles to be on the safe side.

ok well suppose me real question is the second one…i’ll drop this one and ask the second one

I’m no expert, but I would say that whatever would work to sterilize a syringe (whether for heroin or not) would also be adequate to sterilize metal jewelry. Here is how to sterilize a needle.

i’ve sterilized my tapers and plugs and shared them with someone. it’s not that big of a deal i don’t think.. as long as your ears aren’t gross or have had a “blow out” . just keep everything clean.

Yes, but only if you sterilise it properly, by taking it to a piercing shop which will autoclave it for you. The link posted by @Jeruba seems to be based on how to sterilise a needle which hasn’t been used by anyone else. Googling alcohol + blood borne pathogens should give you lots of information indicating that the method outlined there is inadequate.

To be honest, although I understand your desire to minimise your consumption of new jewellery and tapers for environmental reasons it might be best to just buy new for safety reasons and also because I’ve always found it very useful to have smaller sizes of jewellery in reserve. You never know when you might need to downsize for any number of reasons, and having the appropriate jewellery on hand is really useful.