It is Ostap and not Andrei that warns Taras not to make fun of them and their clothes after they return home. Ostap is the more adventurous, whereas Andei's greatest characteristic is the deeply romantic feelings of an introvert.
When the brothers are sitting by the river observing Natalia on the opposite bank, in the front shot they are close together and the rear shot they are apart. Then the front shot reveals them close together again.
The cossacks' "scalp-lock" is not on the back but the front! Only the old cossack is the one that has it correctly. Also Yul Brynner's scalp-lock is very unnatural. It looks like a pony tail and it has too much hair for being only the remaining hair from shaving the rest of the head.