Even though two people get stabbed (PP and the older man), special effects could still be added afterwards to make it look like the boy transforms into the man. This would be similar in concept to when August transformed into a little boy again in “Selfless, Brave, and True.” They had Eion Bailey, who played August, lay on the ground. Next, sequentially, they had Jakob Davies, who plays young August, lay in the same position. Then, the production team blended those two scenes together, added a special effect, and viola, magic! August transformed into a little boy again! So, it could be a very similar technique if PP gets transformed into a grown man, who happens to be played by the same man who has been cast as Rumple’s father (the actor is Stephen Lord).
Oh I’m sure that’s how they’ll do it if in fact PP is Rumple’s father. I’m just saying why would Rumple need to stab Stephen Lord as well? There was a report from someone saying that in the scene Rumple had no problem stabbing PP but he was upset about having to stab the second man (Stephen Lord). If he stabbed PP the boy and they do the switch-up like you described, then after he’s transformed Stephen Lord would still be injured/stabbed and there would be no need to stab him again (cause they were the same character). Unless PP and Rumple’s dad are two separate characters and not one in the same, I don’t see why Rumple would have to stab him a second time.
Idk, it just seems too weird for PP to be his father lol. But ya never know.