I don't believe you can get a call to ring on both phones simultaneously. However, you can create round robin distribution as noted below.
Create a second attendant console user. Modify the existing hunt group by inserting lines for the new attendant user in the sequence that you want calls to alternate.
Example;
Attendant - line 1
Attendant2 - line 1
Attenant - line 2
Attendant2 - line2
etc...
Associate the new phone and attendant console user with the ac user.
Install the attendant console app as you normally would, but using the new attendant user. When this both attendant console users are online, calls will alternate between attendants as configured. When one is not online, it will route all calls to the other.