You can add another user to your machine's server so that they may run lamassu-scripts.
Please be advised that this allows them to create accounts and passwords for the lamassu-admin.
If you are running bitcoind as your machine wallet, they would not have sufficient permissions to run bitcoind commands.
Then, logged in as root in your server, run:
useradd -ms /bin/bash <username>
printf "<public SSH key>" > /home/<username>/.ssh/authorized_keys
Since it would nullify the security of using only SSH keys, do not issue a password for the user with the passwd command.
For a simple list of all users that have home directories (the case for users added through the commands above):
To delete a user and their home directory:
userdel -r <username>