Is it ALL gone?

[Gurthang]

Since Tol Fuin used to be Dorthonion, maybe some of Ungoliant's offspring survived there...

I don't think any of them have survived on the island. In TTT, JRRT states:

But none could rival her, Shelob the Great, last child of Ungoliant to trouble the unhappy world.

So Shelob was the last of the Great Spider descendants of Ungoliant. But how she got to the Mountains of Shadow, is completely unknown to me.