I don't get the individuality thing personally. I think they are individuals no matter how they are dressed. They are who they are & nothing will ever change that.
My girls don't look very similar, but if I buy something & I know they'll both like it, why not just buy it for them both? Just because they are different doesn't mean they don't like the same things.
I knew identical twins who dressed the same but in different colours & they loved it, lol. They liked confusing people We dress them the same as everyone else for school every single day. Doesn't that take away their individuality as well? (Although I know its more than that, but ykwim?)
As long as they both like the clothes & are wanting to wear them, by choice, why would it matter. If they hated the idea & refused, fair enough. Nothing will change who they are inside