There are two options to send an Evite Invitation, Invite More and Facebook.
Regarding forwarding, this is NOT recommended as each invitation sent to a guest has a unique guest ID. When a guest forwards the invitation they received to other people, they will be able to access the invitation as the guest that it was intended for, and any comments or replies made by additional guests will be under the name of the original guest who had forwarded the invitation.
If the host forwards the invitation to other people, it will ask them to sign in since it is a unique host ID for the host of the event.
Instead please use the Invite More or Share Invitation options.
In the "Invite More" option, the host will have to allow guests to invite other people. The guests can then click on the "Invite More" option and add the emails of their desired guests which will be added to the guest list.
In the "Share" option, this is located next to the "Share Invitation" option, and when it is clicked, a link will be copied. Once the link is copied, you can send the link out for guests to view and RSVP.