Please, find my replies below to your questions:
how can I make the thunbnail appear at the bottom of a member list?
If you want the media at the bottom of a member list then you need to use a different action in the previously shared gist.
You can replace the currently used action
bp_directory_members_actions with this one ->
Also, if I want to add a few thumbnails on the member’s profil page?
Well, you can just find available BuddyPress filters on the member’s profile page and reframe the same code to get the random picture we shared with you.
Here, I am attaching a screenshot which can show you the available hooks. You can pick it up according to your requirement.