Of course you can manage your site groups from the Office 365 admin panel, but why use this if you can manage it much faster through PowerShell? To get a an overview of the site groups and its users you can use the PowerShell script below, but before you start you need to connect first to SharePoint Online by using the powershellscript that I have shared earlier.
After that you can use the following PowerShell script in the SharePoint Online Management console
$siteURL = "paste your site url here including https"
$x = Get-SPOSiteGroup -Site $siteURL
foreach ($y in $x)
Write-Host $y.Title -ForegroundColor "Yellow"
Get-SPOSiteGroup -Site $siteURL -Group $y.Title | Select-Object -ExpandProperty Users
The result will be: