Romaji transcription

Need a little advice on how to transcribe the conversations into romaji. If you guys notice any errors, please let me know. It would be much appreciated.

I would ideally like to keep these transcripts as consistent in their romaji spellings as possible by following the real hiragana/katakana spellings.

Right now, I am wondering what the correct transcription for "ja" - meaning "then". "jya", "jaa" or "ja"...??