Go to developer app -settings-quill format area where you can make changes. Your will need to add the fonts in the quill mod files using file manager on hosting. Check Quill site for quill editor set up.

Here is an example of adding font selection to editor menu. It will only show the fonts that are available.

[{ font: [] }],[{ 'header': [1, 2, 3, 4, 5, 6, false] },'bold','italic','underline','clean'],[{ 'align': [] },{'list':'ordered'}, {'list':'bullet'},{'indent': '-1'},{'indent': '+1'},'blockquote',{ 'color': [] }, { 'background': [] },{ 'direction': 'rtl' },'link','image','embed','code-block','emoji','show-html']