"We don't distinguish between any of them" means that we hold all of the messengers to the same high standard. It does not mean that any of them is "better" than the other, in fact, we think that all the prophets and messengers are exact "copies" of one another. They all delivered the same message and had the exact same incidents and events happen in their lives in accordance with their time. We do not distinguish between any of them meaning that they are all the same, no messenger is better than the other and no prophet is better than the other.