If you don't care what groups the users were in, and just want a big ol' list of users - this does the job:
$Groups = Get-ADGroup -Filter {Name -like "AB*"}
$rtn = @(); ForEach ($Group in $Groups) {
$rtn += (Get-ADGroupMember -Identity "$($Group.Name)" -Recursive)
}
Then the results:
$rtn | ft -autosize