TLV9064-Q1: how to deal with the pins which aren't used

Yoshikazu-san,

Here is a blog on this topic. 

https://e2e.ti.com/blogs_/archives/b/thesignal/archive/2012/11/27/the-unused-op-amp-what-to-do

I suggest always having some series resistance when an input is connected directly to a low impedance node (like ground) This is especially important for designs with high currents or high current transients. 1k ohms or more usually is sufficient.