Hi there,
both the Author Box plugin and the GP Social Share plugin ( please note we are not the developers of this plugin ) provide options to use a Shortcode to display them.
You can then use a Hook Element to add the 2 x Shortcodes to your posts:
https://docs.generatepress.com/article/hooks-element-overview/
You will need to select the generate_after_content
hook and set the priority to 2
To change the size of icons you can use this CSS:
#gp-social-share a svg {
width: 20px;
height: 20px;
}