The difficulties of the third book

Last week, I started Sand and Bone to submit to the writing group. I've never written the third book of a trilogy before and I'm struggling with something I never had to deal with before: the previous two books.

The first book is easy, everything is new. Nothing to bring forward. The second book gave me a little more difficulty but it was manageable since I could just make the occasional references to it and move on.

The third is giving me trouble and it seems to be an exponential problem. I have the history of both books to take into consideration. Do I write it as a stand alone novel or with the expectation that readers would read them in order?

I think stand alone is the better approach, though I know very few readers who would start on book three before one and two. Most of them go "oh, book three. Let me start with book one."

The problem with writing it entirely stand-alone is that I have a few things working against me. I have a conlang in the novel (Miwāfu) which uses names that appear to cause some difficulty with native English speakers (e.g., Kanéko, Mioráshi, and Rutejìmo). For me, they make senses but I have a fan-boi obsession with Japanese and a fondness for German (the accents are gender markers). In the first two books, I added 1-2 chapters in the beginning to get the reader used to the names and only introduce 2-3 characters per chapter. One of the questions is, do I do the same thing? I'm not exactly sure since throwing seven characters in the first chapter can be overwhelming, but five them have been described for 130k words in two other books.

The other difficulty is knowledge. The first two books are about events that significantly drive Rutejìmo. It explains his motivations, his struggles, and triumphs. I can't figure out how to hash that in the beginning of the third novel without it becoming an info dump or spreading the revelations over 40k words.

I'm still going to write it, because I've been planning this book for two years, but it has been an interesting experience to say the least. Not sure how it will work out, but I'm hoping it will be a fun read (when it finally gets done).