The proto Indo-European language is only theorized. Greek and Latin are certainly newer and have some similarities to it, but I did not think they were BASED on it. So maybe the proto Indo-Euro language is the bridge between Sanskrit and the western languages, I get confused.
Have you read any of Stephen Knapp’s books? I have many of them, well referenced about ancient history. If you’re interested I’ll freepmail you links to some I have.