Nothing happened when I put in the console command, but I found a solution.
I have tried this, and all the other suggestions.
Even went back to old save, did the situation with Harkon all over, was thrown out, then did the commands.
But no change.
I'm doing this in special edition, but havn't played out the stendarr scenario, so Talon shouldn't be dead.
Any ideas? I just can't play the whole bloodline again since I did too many other stuff in between before going to Volkihar to 'deliver' Serana.