I’m trying to figure out what happened. I can see the account created by your brother, but the invitation is still pending (not accepted). It looks like there are 5 pending invitations to your tree. I just invited myself (under another email) to a tree and it worked ok, and I’m not seeing any invitation errors in the logs, so it’s not an obvious problem.
After you registered your mother, did it take her to the create-tree page or just drop her right into the same empty tree-list page that your brother saw? Could you re-send the invitation and see if that works now that your brother/mother are registered? Or could you ask your brother/mother to forward the invitation email to me, in case they still have it? There’s got to be a problem somewhere; I’m trying to figure out where.