Theme Error - not allowing signups

Using the Buddypress Magazine Theme on my site. It has been hacked a few times.

The sign-up page is no longer able to convert. We have not been able to fix the sign-up page for over a month despite our best efforts. Please help.

1. The site is hosted on a shared server.
2. The site is built on https://premium.wpmudev.org/project/buddypress-magazine-theme
3. The sign-up button now goes to the register page, but does not convert.
4. How can we fix this to be able to sign-up new members.
5. How can we ensure this hack won't happen to us again. Is a dedicated server a way to solve the holes in the theme.