问题在于我们不可以自己设计校服的英语翻译

The question is that we are not allowed to design the school uniform by ourselves.
这里的can not 应该是“不被允许”的意思。

It is the problem that we are not permited to design the school uniforms by ourselves。
or
It is the problem that we are not allowed to design the school uniforms by ourselves。
or
It is the problem that the goverment do not let us to design the school uniforms ourdelves。
原文的“不可以”我理解为不是能力上达不到，而是不被许可。所以翻译成上面那样的句子。

The question is that we could not design the uniform ourselves.

The problem is that we could not design the uniform ourselves.

The problem is that we could not design school uniform ourselves