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If the hair colours are the wrong way around, the second one could be one of the Broken Sword games.
I think Broken Sword is right. I remember the graphics style of the 3D games. Though, I can't find anything about any of the 3D games having a unwinnable condition? I guess it was a different game he had that problem with and I falsely attributed it to the Broken Sword game in my memory.
A point and click with multiple characters that comes to mind is Schizm?
I used to like to watch family members play games when I was young, and there is a couple games I vaguely remember but I don't know what games they are. In the first one, at one point you come across a bunch of snakes in trees, and either the main character or the narrator makes a reference to Harry Potter. I'm not sure what exactly he says, but I think he says something about wishing there was someone there who could speak snake? I think this was a point and click adventure game on the PC
All I remember of the other game is my father being upset because he got stuck in it, and found out they deliberately made it unwinnable if you did something incorrectly earlier in the game, which he had done. It was for the PC, and I'm pretty sure you could switch between a (i think dark haired but not sure) male character and (I think possibly blond?) female character either during the same level or alternate levels, and it may have been a point and click adventure.
I might have gotten a detail wrong because these are really vague memories...