Here's a Powershell function you should be able to use. I only tested it on Windows 10, but I don't think it's using anything that wasn't available in Windows 7.
Function Get-LocalGroupMembers {
[Cmdletbinding()]
Param(
[Parameter(Mandatory=$true)]
[string]$GroupName
)
[adsi]$adsiGroup = "WinNT://$($env:COMPUTERNAME)/$GroupName,group"
$adsiGroup.Invoke('Members') | %{
$username = $_.GetType().InvokeMember('Name','GetProperty',$null,$_,$null)
$path = $_.GetType().InvokeMember('AdsPath','GetProperty',$null,$_,$null).Replace('WinNT://','')
$class = $_.GetType().InvokeMember('Class','GetProperty',$null,$_,$null)
$userObj = New-Object System.Security.Principal.NTAccount($username)
$sid = $userObj.Translate([System.Security.Principal.SecurityIdentifier])
[pscustomobject]@{
Username = $username
Type = $class
SID = $sid
Path = $path
}
}
}