Extension pending approval, if you're interested in beta testing this feature please reach out to email@example.com for the link to the test extension. Support for this feature with the O365 Outlook Add-in Coming Aug 2020.
You can select multiple guests to add to Instant Booker from Gmail or Salesforce. Here are the steps:
1. Compose the email in Gmail / Salesforce and add the recipients
2. Click on the Chili Piper icon
2. You'll see a prompt to select the guests - here you can change the main guest and deselect other guests you don't want to invite to the meeting. Click on Go to calendar
3. The Instant Booker will open and the selected guests are added. That's it, now you can book the meeting!