To be more specific, I'm working on some posters project, and I need mockups. I have one showing one A3 frame with one smart object inside. Now I need mockups for set of 2, 3, 4, 5 and 6 posters. I've tried to make one for set of 3 posters, I duplicated original frame, and when I positioned the first poster and saved, it was shown on all 3 frames. I've tried not duplicating but copying (New Smart Object via copy) smart object and placing it into other 2 frames but with no success. I'm pretty sure this can be done, but I just don't know how. Any help welcome. Thanks.
You're on the right track... Not sure what you're doing wrong.
Right-click on your Smart Object layer and choose 'New Smart Object via copy'.
Double-click on the Smart Object layer thumbnail and place your individual images (File > Place...) behind your frame.
Now editing the contents of either the original or the copy should not affect the other. Here for example are the same frames created this way with different contents: