Like this?
        string path = @"";
        DirectoryInfo dir = new DirectoryInfo(path);
        var files = dir.GetFiles("*.txt");
        if (files.Length >= 2)
        {
        }
solved Check if the two Files exist in the folder
 
Like this?
        string path = @"";
        DirectoryInfo dir = new DirectoryInfo(path);
        var files = dir.GetFiles("*.txt");
        if (files.Length >= 2)
        {
        }
solved Check if the two Files exist in the folder