Granting access to calendar and mailbox of O365 Groups for external users

[jahongir abdurahmonov]

So, we have a lot of consultants (external to organization) working with us. Consultants do not have corporate account. They might use all kinds of public email, gmail, yahoo and etc. I've added some of consultants (@gmail.com) to the Office365 Group as a guest.

Now can I give them access to Group mailbox and Group calendar so that they can see all the messages, and events? 

[#2]

No, guest users can:
(1) Access to the Group SPO Site
(2) Receive messages sent to the Group if they are subscribed
Guest users cannot:
(1) Access the Group Mailbox
(2) Access the Group Calendar

[#3]

What you can do is use a sharepoint tab and add the group calendar webpart! Guest will then be able to see all coming events and also sync them to their calendar!