When working on a lead, you can now select to add your lead directly to an event without leaving the page.
Select the 'three more action' dots at top of the lead details page and select add to event.
Work through the prompts to add them to the right event. Select if you'd like to send the family a confirmation email once registered.
Once complete, you'll see the relevant family members in the event. If you need to update anything else regarding their registration you can select manage booking directly within the event.