I have Beta and The Doctor ranks and i wanted to have both but when i apply one the other is taken off. Can anyone help?

Ranks are essentially just a list of permissions with a fancy title. You can only have one list of permissions, because of how the system is set up, otherwise you'd be getting weird issues with conflicting permissions.

If you want to have both shown ingame, I'd recommend using the set-title command to add the Beta rank there, and having The Doctor as your actual rank as it has more permissions I believe.

You'll need to figure out the colour codes and such for the Beta rank on your own to do this, though, as I'm not familiar with how it looks

Ah, ok. Thank you for your help. 

but there are rank levels. e.g player lowest rank, then beta, and mvp/custom is highest buyable level

idk how vip, vip +, the dcotor and the others compare to each other

 VIP is above donator, VIP+ is the same as The Doctor, The Master, and all of those ranks, as they are just renames I presume, and MVP/Custom Rank is above them.