Re: Adding private key path to when synchronizing a two way delete
                Either  modify the script to construct 
Configure WinSCP PowerShell script to also include a private key
Or encode the key into the session URL:
    
WinSCP GUI can generate such URL for you:
https://winscp.net/eng/docs/ui_generateurl#url
        SessionOptions with SshPrivateKeyPath property, the way I've already shown you on Stack Overflow:
Configure WinSCP PowerShell script to also include a private key
Or encode the key into the session URL:
sftp://user;fingerprint=ssh-rsa-xxxxxxxxxxx...@example.com;x-publickeyfile=C%3A%255Cmykey.ppk@example.com/WinSCP GUI can generate such URL for you:
https://winscp.net/eng/docs/ui_generateurl#url