Before you proceed, you need Spaces installed on your phone.
You might want your members to invite their friends & family to join a Space. With this, they would easily be able to invite them and join the group.
How to enable members to invite users within the Space?
Step 1 - Open the Space in which you want to moderate the members & click on the three-lined menu icon at the top right corner of the screen.
Step 2 - Choose the Settings button
Step 3 - Navigate below and enable Members can invite other users to join the Space.
You are done!