one person in the server has all three skill trees and can use them but for some reason two of us only have one tab

Hi there, Simply Skills removes the default Puffish Skills trees on launch.
To get them back you will need to reenable the default puffish trees via the general config in Simply Skills.
After that, you will need to unlock the trees again with these chat commands:
/puffish_skills category unlock playername puffish_skills:mining
/puffish_skills category unlock playername puffish_skills:combat

You could set "disableDefaultPuffishTrees": to false in the config and delete puffish_skills.dat. see #46