I am able to return for "sitecollectionURL" the primary and secondary admins using the followins PS:
Get-SPSite "sitecollectionURL" | foreach-object{ Write-host $_.Url - $_.RootWeb.Title - $_.Owner.Name - $_.SecondaryContact.Name}
but what I really want is all the ones listed on site settings > site collection owners group (different than primary and secondary site collection admin) and also the site settings > site collection administrators.