you should seen the osomatsu-kun series. I couldn't tell the different since they all have almost the same persona and with the same face expression.
Also here is another advice to tell which is which. that is their hair style on the center of their head.
-Choro has no hair sticking out in the center of his head.
-Jyushi has one strand of hair in the center of his head.
-Ichi has a messy hair.
the other three has the same hair style, but Todo is slightly more curly than Oso and Kara. and has a bigger eyes pupils
To know between Kara and Oso since the both have two hair strand stick out in the center. you just have to listen to their voice and kara has slightly have more bushy eyebrow then oso.