Well, no. But those are all factors that should bring the languages closer together. Unless you mean the Sindar that was universally adopted in Beleriand in responses to Thingol's decree is not the Sindarin in use during the War of the Ring? That actually makes a lot more sense.
That's the point, it was under specific circumstances that they met, and the Dwarves spoke in their language, so the Elves had no reason to change or adapt. Their was no linguistic intercourse. I could see the Dwarves bringing home some Sindarin influences on their own tongue, but since the Elves only kept using their own speech, there was no reason to change it.

This just isn't true.
I don't really see these guys changing much. They're still themselves in events centuries apart. Saruman changes because he is influenced by his hunt for the Ring. Thingol gets more hostile when the Noldor come and when he learns about the Kinslaying. He softens his human policy after Beren. He gets possessive when he accepts the Nauglamir from Hurin (and thus possibly partakes of Morgoth's curse). It's like you can point to a specific thing that informs each new personality trait. I mean, sure, the format doesn't lend itself to these sorts of details, but the guy who fights the first battle of Beleriand doesn't seem too different from the guy who came out of the woods with Maia bride.

The family stuff just suggests that his mind doesn't change, he doesn't forget or grow away from who he was when he and Olwe were together. If his awareness isn't fading or changing priorities, it seems to me that his language wouldn't either. Language and thought are linked. To me, the strong connection to Olwe's grandchildren suggests he has not evolved or moved on from his state of mind since Olwe was a part of his life.