$DG = Get-DistributionGroup | where {

$_.Alias -eq 'Moscow_office'-or $_.Alias -eq 'Saratov_office' -or $_.Alias -eq 'Voronezh_office'

}

$DG | foreach { Get-DistributionGroupMember $_.Alias } | Select Name, DisplayName, PrimarySMTPAddress -Unique | Sort Name