To create internal clan games, it would be easier if you could directly invite your clan members in the invitation menus ("Select Players" and "Add or Remove Players").
If you're in a bigger clan and you don't want to add all 100 members to your friends list, you have to invite every single players laboriously by using the "search" tab. A new invitation tab which shows only your clan members, similar to the friends tab, but maybe with filter options like "rank" or "level" would be the ideal solution.
https://warlight.uservoice.com/forums/77051-warlight-features/suggestions/9148579--clan-tab-in-the-select-players-and-add-or-rem