1 account, 3 devices.

I have 3 Roku devices, 1 in my living room & 1 for each of my kids. They have their own login info for apps & accounts like Plex. However, if I log into my account on the roku devices, they automatically sign me into my accounts on the apps. And when I sign out, they sign me out on all. 

How do I, if it's possible. Link the devices to my accounts, but the login info on the apps operate independently from each other devices? Because I don't want to have to make multiple Roku accounts just to achieve this. 

Thanks