From my understanding, old Latin had the sound /w/ and it later shifted to /v/ while keeping the letter, hence early loan words have “w” like “wine” and later ones have “v” like “vernacular”.

And you are right that the letter was used for the vowel /u/ too, how did I forget about that. So “vv” would be /vu/ (~voo). But I think Latin never had both /w/ and /v/ sound at the same time.