While a popular modding platform, Forge is incompatible with the Win10 edition. If he wants to fight the Wither Storm then This is what I found. As for how to install them I would suggest the official site.
As far as I know there aren't any alternatives. If you really wanna use it you could perhaps try using a Virtual Machine to run windows on your mac. Virtual Box is free. Can't guarantee a good performance or that it'll work, but may be worth a try.
I’m not aware of even mods that can do this, bu I do know of some spigot plugins that can. Skoice uses a discord bot for the voice chat, so that may sound nice. There’s also proximity chat which uses text I believe.
I can try to help; please provide more details:
Please post the entire crash log (or logs) on http://gist.github.com (never post logs in Reddit self post text!) and share the URL for the submitted log.