In the onRollButton_pressed function, you disable the button on the server side (because of the if gettree().isnetwork_server()).
The problem is, all instances of your game (the server and all the clients) have a different scene tree, so when you disable a button on the server, nothing happens on the client.
Tho fix this problem you need to do 2 things:
1) On the server, instead of doing
You need to do a rpc_id to the corresponding player and inside the remote function (on the client) you need to disable the button. You also need to do the same thing for enabling the button
2) When you are doing a multiplayer, game you need to remember 1 rule: Never trust the client
This means you need to keep track of which player is able to click the button and which isn't, on the server.
When a player do a rpc_id to the server when he click the button, the server must test first if the player is actually able to click the button (in case of someone modifying there game to cheat)