It looks very much as if you've set your default browser to be Chrome, and your Home Page (which is not the same thing) to be Yahoo.
Just open the browser, then go to the site (such as google.co.uk) that you want for you home page.
Then click the 3 bars icon at the top right of the browser and choose settings.
In the On start-up section, there should be a dot next to "Open a specific page..."
To the right of that it says "set pages" Click on that and then click "Use current page"