No, Yes, No
References:
https://community.spiceworks.com/topic/2150016-can-you-apply-a-retention-policy-to-users-within-a-group-on- Distribution lists and mail-enabled security groups will be expanded so the policy will apply to all the mailboxes in the group. Only the mailboxes that are currently members of these groups will be covered by the policy. Mailboxes added to these groups later won't be covered, but ones that are removed later will still be covered.