See if this works for you.
(Get-Group "SelectedUsersGroup").members |
Get-Recipient |
ForEach-Object{
Try{
Get-CsOnlineUser -Identity $_.userPrincipalName -ErrorAction Stop
Grant-CsTeamsVideoInteropServicePolicy -PolicyName PolycomServiceProviderEnabled -Identity $_.userPrincipalName -ErrorAction Stop
}
Catch{
# you can do something here if you like for group members that aren't enabled
}
}