>>If yes, you may have to calculate relative weight (or what's the right term? "удельный вес" in Russian) of each duplicate to the total number of records removed from each particular table...
>>
>>Anyway, let's see, if this is the exact problem you're trying to solve, because now I can see the complexity.
>
>Why complexity? You calculate number of duplicates that needs to be deleted, then you calculate the deletion number for each of 4 tables, and then you scan and delete in each table counting delete total until you get the number. Obviously, during deletion you should reduce the total duplicate counter to keep the last record intact.

What if we also want to somehow keep the original table sizes proportions?

I want to first hear the exact problem definition with some samples, then we can think of a solution.