Hi Phil,
I hope you are well today and thank you for your questions.
1 / How to add in the footer a logo and remove << theme colorlib proudly powered by wordpres >>?
To achieve this you have to develop custom code in the child theme of Activello theme as shared in the following topic.
https://colorlibsupport.com/t/change-theme-by-colorlib-powered-by-wordpress-in-footer/#post-100985
2 / I use Jetpack gallery. In a page the gallery is the width of the page whereas in an article it is not the case. How to make the gallery the full width of the article ?
You can increase content width to display Gallery full width using any of the following solutions.
Best Regards,
Movin