If he takes too much time loading it's because his long loading times. As mentioned modpack it's heavy. Removing graphical mods will help.

my brother couldn't join my great campaign lobby with this

Guys, i am literally doing a play trough with theese mods. The modpack is very heavy, and requires a 12 GB Vram graphics card almost. Try to disable heavy graphics mods.

SatansHousewife, Same here. Fresh install and only these mods

Strange, i played some time ago and worked fine. Unsubscribe and resubscribe maybe something got corrupt.

Loading into a campaign, the loading bar gets about half way, then crashes after 10 minutes. Not new to modding, only using this collection, doesn't seem to work for me.

Usually it's better due to the fact that you might have older mods in your data folder.

Fresh install, meaning I have to uninstall and reinstall the game before subscribing to the mods?