A good test for your party would be to create a blank campaign and send them the link for it. If they can connect to that without any problems, then you might want to look into whether you can trim down your campaign so there's less for your players' computers to load. In your campaign details page, you have the ability to duplicate your campaign. With duplicates, you can split up a campaign into smaller, more manageable, data chunks for your players to load.
If they can't load a blank campaign, then there might be a bug or a glitch somewhere that we'll need to dig out.
