To grant other people developer or staff access on your Laddr instance, they should first register their own account through the standard signup process build into the site. If you have separate staging and live sites they will need to register for both separately.
Once they have registered their account, find them on the /people page and open their profile. If you’re logged into your own staff account you will see an “Edit Profile” link. Follow that and then use the “Account Level” dropdown. If you grant the “Developer” account they will be able to access /develop and make changes to the site’s source code.