setting up shell access for other users

[sports]

I have set up a couple of subdomains to allow contract techs to upload files and test them for my websites. Trouble is, turning access on and off is being done in Linus and not Plesk. I tried changing permissions in Plesk but it said changes not allowed. What is the right way to create shell access for my domain, grant someone access and be able to turn it off and on as needed?