Except it didn't last very long. In 1803 or SCOTUS gave themselves the power to declare something to be constitutional or not. Why Jefferson or whoever was president at the time didn't ride up the SCOTUS building with the local militia to kick them all out is beyond me.
Yeah I get about tired of hearing how they're the "final word" on various issues, but even they can be overrode on a constitutional issue if 2/3 of the states vote for a new amendment, but good luck getting that type of agreement on something these days.
No. By seeing what they are doing and comparing it to the what the constitution permits and doesn't permits which is plain language and NOT open for interpretation. For example if the legislative branch tries to give the military orders during a time of war(or any other time for that matter). That is something they can't do and the courts can tell them to stop it.
No, they were never co equal. The founders feared that a judiciary with no citizen control could become an imperial judiciary. It's ironic that it was Jefferson who got tricked into forming it.