Hello,
Thank you very much for choosing our theme and for contacting us.
You can disable the double title in the Theme Settings > Product page https://prnt.sc/sstkqg
You can change the font size by means of the Advanced typography option, which allows to choose the item from a drop-down or insert your custom CSS class. Please navigate to the Theme Settings > Typography > Advanced Typography.
Here is the documentation providing more detailed instructions: https://xtemos.com/docs/basel/advanced-typography-settings-2/
Best Regards