How do I set a constant in setup() that I can use in loop()?
You can't, and there's other things wrong with your code.

int sensorValue1 = analogRead(A0);  
int sensorValue2 = analogRead(A1);  


Calling functions from the global scope is an incredibly bad idea.  Those are run before the board has been properly initialized, and the results you may get from it are not guaranteed in any way, shape, or form.  Instead you must call functions like analogRead() from within another function, like setup(), or loop().

As for const - a const is just that - a constant value that can never change.  You can only assign a value to it at the moment of creation.

And that means that you can only use it within the scope it was defined within.  As you can't do that in the global scope (see above) then you cannot use a constant.

So just use a normal global variable.  It will only change when you tell it to change.  Using a const only makes sense when you have a numeric literal that you want to refer to by name. Using const doesn't protect the variable from being changed at run-time by memory leaks, etc, it just protects it from attempts to modify it at compile time - and if possible replace it with the numeric literal that it refers to.

So in summary just use:

int sensorValue1;
int sensorValue2;
int p1;
int t1;

void setup() {
    sensorValue1 = analogRead(A0);
    sensorValue2 = analogRead(A1);
    p1 = (1.09512*sensorValue2-22.105)*133.3225;
    t1 = (-0.08126*sensorValue1+65.6597)*274.15;
}
... etc ...


HOWEVER: Your program methodology is also completely flawed.  You read the analog values once, and do calculations with them once, then repeatedly display the same values over and over again.

You must perform a new analogRead() of your sensors every iteration of loop() in order to update the values in your variables.