King Naugladur, dealing first with what you had to say about Nargothrond and the Nauglamír:
Mim had inheritance claim to the caverns of Narog where Nulukkizdin and later Nargothrond lay. But, Turin had promised Mim a "danwedh" (ransom) in case he stumbled upon treasure and he took the hoard of Nargothrond as his promised reward. Moreover, one could argue that Mim's inheritance covered everything found inside the halls of Nargothrond, including the treasure. And, since Mim had no close kin, as the Petty-Dwarves were wiped out, the treasure had to go to members of the race he belonged to. What do you think?
We appear to agree that Mîm had at least an arguable claim regarding Nargothrond. But that would not necessarily include a claim on any of the hoard. There is a distinction in law between 'real property', i.e. immovable property, such as land and any improvements made to it, and 'personal property', i.e. movable property, that can be moved from one place to another. Nargothrond is real or immovable property, while the hoard is personal or movable property. Having an arguable claim on the first does not mean the dwarf has one on the second.
I don't see the issue of Túrin's promise of compensation to Mîm for killing one of his sons as relevant here. You can't give away what isn't yours;
and I have read nothing that indicated Túrin had
any claim of ownership to any of the hoard. Again, the hoard belonged to Finrod, and on his death would arguably go to his surviving relatives, including Thingol. At least Húrin gave part of the hoard to someone with an arguable claim to it, instead of keeping it for himself.
Looking at what you said second, about the Silmaril:
As for the Silmaril, Thingol was not involved in the dispute between Feanor and the Teleri of Aman. Moreover, he had already issued his countermeasure, having banned Quenya within his realm. The Silmaril did not belong to him and he had to give it.
How could Thingol
not be involved in a dispute where the people of his brother Olwë were massacred and their property stolen?
I again agree that he still should have returned the Silmaril to the sons of Fëanor, as it was rightfully theirs, and would negate some of the effects of the Oath.
In answer to what you asked here:
PS. Do you know how can I put accents over the letters (such as the umlaut over "e" in the name of Feanor, etc.)?
I tend to open another web page and copy and paste the relevant names into the message box.