Download, Upload and Move FTP Files PowerShell

I'm new with PowerShell and I'm working on a Script that has to download files from different routes on a Linux machine by FTP in other routes of a Windows machine and also move them to another destination within Linux, basically like this:

So far for what I have researched I have to make the connection by "webclient" and the code that I have is the following:

#Linux source folders 
$source1="/source1/"
$source2="/source2/" 
$source3="/source3/"     

#ftp server 
$ftp = "ftp://192.168.0.2/../../" 
$user = "usu1" 
$pass = "usu1"  

$webclient = New-Object System.Net.WebClient 

$webclient.Credentials = New-Object System.Net.NetworkCredential($user,$pass)  

#Download from source1 folder 
foreach($item in (Get-ChildItem $source1 "*")){ 
    "Uploading $item..." 
    $uri = New-Object System.Uri($ftp+$item.Name) 
    $webclient.DownloadFile($uri, $item.FullName) 
 }

#Download from source2 folder 
foreach($item in (Get-ChildItem $source2 "*")){  
    $uri = New-Object System.Uri($ftp+$item.Name) 
    $webclient.DownloadFile($uri, $item.FullName) 
 }

#Download from source3 folder 
foreach($item in (Get-ChildItem $source3 "*")){ 
    $uri = New-Object System.Uri($ftp+$item.Name) 
    $webclient.DownloadFile($uri, $item.FullName) 
 } 

And I get the following error:

Get-ChildItem : No se encuentra la ruta de acceso 'C:\source1\' porque no existe.
En línea: 16 Carácter: 23

As far as I can see, it tries to search in Windows.

Thank you in advance for the help you can give me.

Greetings.