Using FFmpeg can I merge three different videos using overlap and overlay in one instance?

Question

I'm quite new to FFmpeg, so please bear with me.

I find myself in a situation where I have:

An intro video A main video An outro video Desired effect:

The intro video has an alpha channel that at the end functions as a transition as it reveals the main video. An overlap in the concatenation would help this happen.

The last 20 seconds of the main video need to have the frame scaled down and overlaid in a corner of the outro video.

Also important to note that there are versions the main video with different language audio channels, so I would like to create a merged output for every channel.

What is the procedure? Is this possible to do in one instance or in one go? Can I batch process?

FFProbe gives me the following...

For videos with one language:

Input #0, mov,mp4,m4a,3gp,3g2,mj2, from 'SINGLELANG.mp4':
  Metadata:
    major_brand     : mp42
    minor_version   : 0
    compatible_brands: mp42isom
    creation_time   : 2017-03-23T14:24:12.000000Z
  Duration: 00:10:52.84, start: 0.000000, bitrate: 2423 kb/s
    Stream #0:0(und): Video: h264 (High) (avc1 / 0x31637661), yuv420p, 852x480 [SAR 1:1 DAR 71:40], 2031 kb/s, 25 fps, 25 tbr, 25k tbn, 50 tbc (default)
    Metadata:
      handler_name    : Telestream Inc. Telestream Media Framework - Release TXGP 2016.50.195670
      encoder         : AVC
    Stream #0:1(eng): Audio: aac (LC) (mp4a / 0x6134706D), 48000 Hz, stereo, fltp, 381 kb/s (default)
    Metadata:
      handler_name    : Telestream Inc. Telestream Media Framework - Release TXGP 2016.50.195670

For videos with more than one language:

Input #0, mxf, from 'MULTILANG.mxf':
  Metadata:
    uid             : e4cf0a91-0e3c-11e7-9129-d89d671392e0
    generation_uid  : e4cf0a92-0e3c-11e7-bf5f-d89d671392e0
    company_name    : Telestream
    product_name    : Flip Technology
    product_version : 3.0
    application_platform: win32
    product_uid     : ffeeddcc-bbaa-9988-7766-554433221100
    modification_date: 2017-03-21T13:47:15.000000Z
    material_package_umid: 0x060A2B340101010501010D12130000002262F5023378058082B6D89D671392E0
    timecode        : 00:58:43:05
  Duration: 00:17:12.00, start: 0.000000, bitrate: 57535 kb/s
    Stream #0:0: Video: mpeg2video (4:2:2), yuv422p(tv, bt709, top first), 1920x1080 [SAR 1:1 DAR 16:9], 50000 kb/s, 25 fps, 25 tbr, 25 tbn, 50 tbc
    Metadata:
      file_package_umid: 0x060A2B340101010501010D121371EEFF0E62F50233780580F599D89D671392E0
      file_package_name: Source Package
      track_name      : Track 1
    Stream #0:1: Audio: pcm_s24le, 48000 Hz, 2 channels, s32 (24 bit), 2304 kb/s
    Metadata:
      file_package_umid: 0x060A2B340101010501010D121371EEFF0E62F50233780580F599D89D671392E0
      file_package_name: Source Package
      track_name      : Track 2
    Stream #0:2: Audio: pcm_s24le, 48000 Hz, 2 channels, s32 (24 bit), 2304 kb/s
    Metadata:
      file_package_umid: 0x060A2B340101010501010D121371EEFF0E62F50233780580F599D89D671392E0
      file_package_name: Source Package
      track_name      : Track 3
    Stream #0:3: Audio: pcm_s24le, 48000 Hz, 2 channels, s32 (24 bit), 2304 kb/s
    Metadata:
      file_package_umid: 0x060A2B340101010501010D121371EEFF0E62F50233780580F599D89D671392E0
      file_package_name: Source Package
      track_name      : Track 4
    Stream #0:4: Data: none
    Metadata:
      file_package_umid: 0x060A2B340101010501010D121371EEFF0E62F50233780580F599D89D671392E0
      file_package_name: Source Package
      track_name      : Track 5
      data_type       : vbi_vanc_smpte_436M
Unsupported codec with id 0 for input stream 4