The free online version of SketchUp doesn't allow scaling apparently, I downloaded the pro version as a trial and I was finally able to scale my two projects, from there I was also able to switch them to .stl by lightening them as much as possible, And Solidworks was kind enough to open them to me in surface, on which I can finally trace my faces on top of the existing surfaces and then hide them, with a sewn surface of the whole assembly and the thicken function, I finally have everything I need!!
Thank you so much for the time you took to help me!!