> To which input should I insert both an active di-box with a passive
> guitar and a passive dibox with an active guitar?

MIC input without phantom power (unless the active DI box is powered by phantom power).

> To which inputs should I insert all the rest of the guitars without
> di-box and different types of the pickups?

INST input.

> How can my 3-4 inputs be line and mic at the same time, when those are
> absolutely different input levels?

These are combo connectors, the XLR connector is a mic level input, the TRS connector is a line level input.

> What happens to my inputs when I swich on a phantom power? Are they
> becoming a line inputs so they can handle amplified mic signal?

When you switch on phantom power, the phantom power is activated on **all** mic inputs. A phantom powered mic does not deliver a line level signal.

As amazing as it may seem, the [owner's manual][1] provides useful information.


  [1]: https://pae-web.presonusmusic.com/downloads/products/pdf/Studio_26_and_68_OwnersManual_EN_19062017.pdf