In the requirement of שביתת כלים if one is a partner with a non-religious Jew in a workshop; would I be correct in assuming it is only items that belong exclusively to you that would require not being used. I.e. you would not be called upon to force the other person to not use items co-owned (if possible).
The halachach is that a person is allowed to lend his tools and vessels to a non Jew who will use them on Shabbos.
O:CH 241:1 & 252:5