how to justify the "rough and tumble" used in this sentence?
The pronouns it and that are referring to different things:
Our clothing is designed to take the greater "rough and tumble" that they expect the boys to give it.
In other words:
our clothing → it
the greater "rough and tumble" → that
Of course, you could drop the use of it (and even the use of that), but the sentence would need to be rephrased slightly.
Here is one possibility:
Our clothing is designed to take the greater "rough and tumble" they expect from the boys.