The person in question is deceased, so really, consent is out of the question. But I do have DNA samples in the form of a licked envelope. Do commercial DNA tests like 23andMe or Ancestry.com follow up this kind of requests?
Is it illegal to sequence the DNA of a person without their consent?
Well, think of it this way. That’s pretty much what forensic labs are doing when handling samples containing DNA evidence. Did the “criminal” consent to being profiled? Guess not.
Then there are all these other companies that do “cheating” tests, where they ask for samples like hair on a brush or some form of fluid stain. It’s a bit far fetched if you ask me, but it definitely seems it’s not illegal to send in someone else’s DNA than your own.
Your licked enveloped story sounds cool 
Please follow-up if you send the evidence.