and Nienor looks like Hurin (Tall and blonde).
and her late older sister Urwen called Lalaith.
I imagine it is next to impossible to travel around Beleriand at this point. Brethil is the only ’safe haven’ for Edain, and that’s not saying much. So even if Niniel is curious about her past, going out to seek it is not straighforward. And she feels there is a shadow in her past this might factor into her not wanting to find out. With all of the orcs around, she may assume that everyone else is dead. I think this is what the men of Brethil in general are going to think.
But Doriath is just over the river and she has no known trouble with them. Turin himself would not go there, of course, but she very much can. And elves are a source of gossip and do know stuff and beyond that they often are clairvoyant. Any companion could take Niniel to an elvish border guard to ask some questions - not much trouble doing that.
EDIT: [o.k. - this could be handled by showing an attempt of doing just that that is hindered by some mishap on the way and has to be given up on...]
'serves him right, the fool.'
That is the problem I see with the story. The irrationality of both Turin and Nienor is so grand at times that there is a feeling that their early death was unavoidable anyway and at least they now are no longer in the position to harm any more surrounding people by their stupidity. The unborn child, were it to inherit the stupidity of its both parents - is probably better off dead too. Their tragedy seem self-made by their both simple refusal to think...
So there is the risk the audience would actually feel relief that Turin and his sister are finally dead and their self-made tragedy is over... This is what the expression "to dumb to live" means.
Of course there is an ancient idea going back to ancient Greece that "whom a god wishes to ruin, he first deprives of reason/when a god will punish, he will first take away the understanding."
but imho that would make Morgoth far too understanding of human nature and how to corrupt it...
As far I understand Morgoth is not that far into human psychology, that far more becomes Sauron's area of expertise and that later in time.
Random Brethil human seeing some people on the road isn't going to observe closely and then figure out later that their de facto chief's new girlfriend is very familiar...
It is general war time. There have to be Brethil scouts watching the highway. The scouts' duty is to observe and identify foreign people passing by and to find out their purpose. Those are usualy trained and/or naturally gifted fot that purpose. The journey along Brethil takes about a day on horseback. You have to make breakes for the horses and people to rest and drink. Not a distance you could run through with hoods on unrecognised or unnoticed.
People would recognise Morwen either by remembering her or by her entourage. She would not travel that far with her daugther alone, she would have some of her servants and men from her household with her. There are not so many noble houses among humans as yet to lose track of them...