Remodel 6 parts in SolidWorks

We have 6 STEP files of technical parts and we need to remodel them in SolidWorks 2020 or pre-version. These models must be parametric and editable afterwords.

Must be done from scratch and not using FeatureWork option from SW.

The seat example would be 3 parts (seat, back and head rest) with some details on the back side.

Thanks,