In the Yuan-ti temple, to go to the western area, do I have to go through that crushing trap or is there another way? Also, where do I find the fifth pillar? I got the four outside, can anybody help me please?

One of the pillars is broken, and you find it inside the temple.

If you're doing the kill all the Yuan-ti option, yes you do have to go through the crushing walls. It's the only way to get to the lower areas

Just search the area around the wall to find the trap to disarm it. There are also several floor saw type traps around the temple and these can be disarmed as well.

The broken "fifth pillar" is almost directly east of the enterance stairs. If you go directly east through the first room to your right, the one with the acid bath trap, then then the enterance to the room with the pillar is in the southeast corner of the next room.