How do I prevent Google from overriding Safari as the default browser?

Do you have Google set as your Search Engine. If that is the case, you will get results from Google and the websites and maps used in those results will be Google centric, often times with a popup to sign into Google.

Check at Settings > Apps > Safari > Search Engine.

I assume you are talking about Google’s Chrome browser. I’m not sure why you want it on your machine, but as you know it’s a headache. I prefer Firefox as an alternative browser.