Allow comment possibilities by user role

Hello,

I use WordPress for years and I’m pretty good in HTML and CSS but my PHP level is very low.
For a particular website, I must define comment possibilities depending on user role. I’ve been searching for hours, first in existing plugins and after on google and here to find another solution but I found nothing. So, maybe you could help me (I’ll be so grateful to you!)…

[I’m running WordPress 5.1.1]

There’s what I need to have with comments on the website :
1) Customer
A “customer” can post new topics. He can see comments content on his topic but elsewhere he can only see who have comment. He can’t post a comment, only reply to comments on his topic.
2) Subscriber
A “subscriber” can’t post new topics. He can see its comments but he canot see other’s comments, he can only see who have comment, not the content of the comment. He can comment on any topic but but can’t reply to a comment except to its own comments.
3) Admin
An “admin” can do everything, of course
4) Simple visitors
A user who’s not logged-in is like a subscriber who can’t comment (he can see topics and see who’ve commented)

Is it possible to do this by editing WordPress PHP files ?

In advance, thanks a lot for your replies !

The page I need help with: [log in to see the link]