Do not, under any circumstances, share your login information with other people. It’s that simple. There is no reason to ever give your password to anyone else.
If you want other people to be able to start your server, use the Share Access feature.
It's not exactly my server, it's a shared server on a shared Aternos account (not the one I am currently on).
Try the /team command.
It's indeed this command to configure teams, so problem resolved; thanks!