The way I see it a 5" scope plus a 5" scope = still less image brightness and thus SNR on extended objects and less depth on point sources than a single 8" scope..let alone a 10" or 12"...?
Given you are talking one shot colour it may be a waste of effort and more expensive in the end
ie just get an 8" or 10" scope instead.
If you were talking doing LRGB where one scope did the Lum and the other the RGB, maybe you would be on to something
Mike