Is it possible to unlock an iPhone with dead person's fingerprint?

No.

Probably best to assume a biometric unlock is possible.

If a Touch ID or Face ID unlock is a potential threat to you:

• If the (is not yours) iPhone contents are a potential legal problem for you, contact your lawyer now.
• If the contents of the (is yours) iPhone are a potential problem, use a long and robust passcode, not biometrics.

There are articles speculating on these possibilities including one in Forbes, but with a decided lack of documentation.

Also for completeness: How to request access to a deceased family member’s Apple Account - Apple Support

I don't believe there are any published statistics on this morbid thought. But theoretically, a deceased person's finger "could" be used to unlock a phone which is Touch ID capable. But that would be dependent on how long they have been deceased.

prabhu777 wrote:

after 6-7 hours of dead, with finger, can they open?

I doubt it. But I can neither confirm or deny. It's totally morbid in the first place. And I won't continue replying to this question.