Why would it be problematic for the legislative or executive branches to interpret the laws too?

The legislative branch makes the laws, the executive branch enforces the laws, and the judicial branch interprets the laws. Acting as a check on each other, the legislative branch cannot make a law that would be unenforceable or unconstitutional. The executive branch cannot make up its laws to enforce; only the legislative branch.

both believe in many god or polytheism

both built temples that they worshiped in both civilization's god were humanoid

both groups made religion a large portion of their lives

both believe in one religion throughout

the dead were buried with items for the afterlife

a. always outside of government control.