The next code shows how get the parent process filename of a PID, using Delphi.

uses
  Psapi,
  Windows,
  tlhelp32,
  SysUtils;

function GetParentProcessFileName(PID : DWORD): String;
var                               
  HandleSnapShot      : THandle;
  EntryParentProc     : TProcessEntry32;
  HandleParentProc    : THandle;
  ParentPID           : DWORD;
  ParentProcessFound  : Boolean;
  ParentProcPath      : PChar;
begin
  ParentProcessFound := False;
  HandleSnapShot     := CreateToolhelp32Snapshot(TH32CS_SNAPPROCESS, 0);
  GetMem(ParentProcPath, MAX_PATH);
  try
    if HandleSnapShot <> INVALID_HANDLE_VALUE then
    begin
      EntryParentProc.dwSize := SizeOf(EntryParentProc);
      if Process32First(HandleSnapShot, EntryParentProc) then
      begin
        repeat
          if EntryParentProc.th32ProcessID = PID then
          begin
            ParentPID  := EntryParentProc.th32ParentProcessID;
            HandleParentProc  := OpenProcess(PROCESS_QUERY_INFORMATION or PROCESS_VM_READ, False, ParentPID);
            ParentProcessFound:= HandleParentProc <> 0;
            if ParentProcessFound then
            begin
                GetModuleFileNameEx(HandleParentProc, 0, PChar(ParentProcPath), MAX_PATH);
                ParentProcPath := PChar(ParentProcPath);
                CloseHandle(HandleParentProc);
            end;
            break;
          end;
        until not Process32Next(HandleSnapShot, EntryParentProc);
      end;
      CloseHandle(HandleSnapShot);
    end;

    if ParentProcessFound then
      Result := ParentProcPath
    else
      Result := '';
  finally
      FreeMem(ParentProcPath);
  end;
end;