What tools do you use in academia to jointly review a thesis?
This is a good question and I don't want to discourage you, but let me explain what you will likely find most of the time.

They each already have a preferred way of giving you their feedback and some or all of them will not want to use whatever tool you choose.  Since they are doing you a favor, you will need to respect their preference.  For instance, I prefer to take a hard copy and a red pen and go to a coffee shop or library in order to focus.

Also, when I review a thesis I do not want to see comments from other reviewers before I form my own opinion.