Hello,
The manager is not notified by email about a new approval, only visible in portal
Are you sure that the manager of the requestor (the user who initiated the custom command execution) has an address specified in the Email property? Are other email notifications delivered properly?
Once the Manager approves it, the whole action is approved How can I build a flow of two approvers? First manager, then owner of target group
It can only be done using a separate business rule triggering Before adding a member to a group. For details, have a look at the following tutorial: https://www.adaxes.com/help/RequestApprovalForAddingMembersToGroups. Finally, you should have something like the following the following: